<?xml version="1.0" encoding="UTF-8"?>

<!--XBRL Document Created with Wdesk from Workiva-->
<!--Copyright 2020 Workiva-->
<!--r:9e51504d-446f-4acc-a0cd-acabcf214b8d,g:b70a877d-1690-4aed-9062-e2b85cb52ee3-->
<link:linkbase xmlns:link="http://www.xbrl.org/2003/linkbase" xmlns:xlink="http://www.w3.org/1999/xlink" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns:xbrldt="http://xbrl.org/2005/xbrldt" xsi:schemaLocation="http://www.xbrl.org/2003/linkbase http://www.xbrl.org/2003/xbrl-linkbase-2003-12-31.xsd">
  <link:arcroleRef arcroleURI="http://xbrl.org/int/dim/arcrole/all" xlink:type="simple" xlink:href="http://www.xbrl.org/2005/xbrldt-2005.xsd#all"/>
  <link:arcroleRef arcroleURI="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:type="simple" xlink:href="http://www.xbrl.org/2005/xbrldt-2005.xsd#hypercube-dimension"/>
  <link:arcroleRef arcroleURI="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:type="simple" xlink:href="http://www.xbrl.org/2005/xbrldt-2005.xsd#dimension-default"/>
  <link:arcroleRef arcroleURI="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:type="simple" xlink:href="http://www.xbrl.org/2005/xbrldt-2005.xsd#dimension-domain"/>
  <link:arcroleRef arcroleURI="http://xbrl.org/int/dim/arcrole/domain-member" xlink:type="simple" xlink:href="http://www.xbrl.org/2005/xbrldt-2005.xsd#domain-member"/>
  <link:roleRef roleURI="http://www.cmc.com/role/CoverPage" xlink:type="simple" xlink:href="cmc-20200229.xsd#CoverPage"/>
  <link:definitionLink xlink:role="http://www.cmc.com/role/CoverPage" xlink:type="extended" id="ic4de14ed287148cea9d6fcde2dbdb690_4d512e7a-125e-4912-88b8-0f8387004082"/>
  <link:roleRef roleURI="http://www.cmc.com/role/CONDENSEDCONSOLIDATEDSTATEMENTSOFEARNINGSUNAUDITED" xlink:type="simple" xlink:href="cmc-20200229.xsd#CONDENSEDCONSOLIDATEDSTATEMENTSOFEARNINGSUNAUDITED"/>
  <link:definitionLink xlink:role="http://www.cmc.com/role/CONDENSEDCONSOLIDATEDSTATEMENTSOFEARNINGSUNAUDITED" xlink:type="extended" id="ia5f5121e0c0d48a6816acd4ead618729_ae38f111-569e-4057-b278-1f9caea4abc9"/>
  <link:roleRef roleURI="http://www.cmc.com/role/CONDENSEDCONSOLIDATEDSTATEMENTSOFCOMPREHENSIVEINCOMELOSSUNAUDITED" xlink:type="simple" xlink:href="cmc-20200229.xsd#CONDENSEDCONSOLIDATEDSTATEMENTSOFCOMPREHENSIVEINCOMELOSSUNAUDITED"/>
  <link:definitionLink xlink:role="http://www.cmc.com/role/CONDENSEDCONSOLIDATEDSTATEMENTSOFCOMPREHENSIVEINCOMELOSSUNAUDITED" xlink:type="extended" id="i24d6f3d63cf845038edf55c53bceddc2_d5950199-ff34-4cef-b506-d7f882c13efc"/>
  <link:roleRef roleURI="http://www.cmc.com/role/CONDENSEDCONSOLIDATEDBALANCESHEETSUNAUDITED" xlink:type="simple" xlink:href="cmc-20200229.xsd#CONDENSEDCONSOLIDATEDBALANCESHEETSUNAUDITED"/>
  <link:definitionLink xlink:role="http://www.cmc.com/role/CONDENSEDCONSOLIDATEDBALANCESHEETSUNAUDITED" xlink:type="extended" id="iabaa37731b254824add59057d5013eb8_eac393fe-8cda-462a-bca0-97c67ed0c1d9"/>
  <link:roleRef roleURI="http://www.cmc.com/role/CONDENSEDCONSOLIDATEDBALANCESHEETSUNAUDITEDParenthetical" xlink:type="simple" xlink:href="cmc-20200229.xsd#CONDENSEDCONSOLIDATEDBALANCESHEETSUNAUDITEDParenthetical"/>
  <link:definitionLink xlink:role="http://www.cmc.com/role/CONDENSEDCONSOLIDATEDBALANCESHEETSUNAUDITEDParenthetical" xlink:type="extended" id="ic51a847b5dda4b61b34adaaf3e0f8ee8_c4f5a631-7de2-4ffb-a687-e550f35f0c80"/>
  <link:roleRef roleURI="http://www.cmc.com/role/CONDENSEDCONSOLIDATEDSTATEMENTSOFCASHFLOWSUNAUDITED" xlink:type="simple" xlink:href="cmc-20200229.xsd#CONDENSEDCONSOLIDATEDSTATEMENTSOFCASHFLOWSUNAUDITED"/>
  <link:definitionLink xlink:role="http://www.cmc.com/role/CONDENSEDCONSOLIDATEDSTATEMENTSOFCASHFLOWSUNAUDITED" xlink:type="extended" id="ib69fb0c6d6444e8c930e2c1113f44e33_4974d454-d854-4219-9bd2-fa3ac7e246c0"/>
  <link:roleRef roleURI="http://www.cmc.com/role/CONDENSEDCONSOLIDATEDSTATEMENTSOFCASHFLOWSUNAUDITEDParenthetical" xlink:type="simple" xlink:href="cmc-20200229.xsd#CONDENSEDCONSOLIDATEDSTATEMENTSOFCASHFLOWSUNAUDITEDParenthetical"/>
  <link:definitionLink xlink:role="http://www.cmc.com/role/CONDENSEDCONSOLIDATEDSTATEMENTSOFCASHFLOWSUNAUDITEDParenthetical" xlink:type="extended" id="idc65ee638e874cf9b54c9885418056e2_0b27da1f-3480-4c48-a1f1-f56e4c375814"/>
  <link:roleRef roleURI="http://www.cmc.com/role/CONDENSEDCONSOLIDATEDSTATEMENTSOFSTOCKHOLDERSEQUITYUNAUDITED" xlink:type="simple" xlink:href="cmc-20200229.xsd#CONDENSEDCONSOLIDATEDSTATEMENTSOFSTOCKHOLDERSEQUITYUNAUDITED"/>
  <link:definitionLink xlink:role="http://www.cmc.com/role/CONDENSEDCONSOLIDATEDSTATEMENTSOFSTOCKHOLDERSEQUITYUNAUDITED" xlink:type="extended" id="i56e285f4cc2d46d48b30f9c27a18f58a_91a0b7bd-1e9a-4e6c-9a60-6f42cb98cef9">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementLineItems_ac96e3cf-5305-4a78-83a4-55f20c4bada4" xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_StatementLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_c0c423b2-ed24-4d49-bccd-0cf3d76c3416" xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_IncreaseDecreaseInStockholdersEquityRollForward"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_ac96e3cf-5305-4a78-83a4-55f20c4bada4" xlink:to="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_c0c423b2-ed24-4d49-bccd-0cf3d76c3416" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockholdersEquityIncludingPortionAttributableToNoncontrollingInterest_0bbda6ec-9e57-4da0-a808-b443e9567036" xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_StockholdersEquityIncludingPortionAttributableToNoncontrollingInterest"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_c0c423b2-ed24-4d49-bccd-0cf3d76c3416" xlink:to="loc_us-gaap_StockholdersEquityIncludingPortionAttributableToNoncontrollingInterest_0bbda6ec-9e57-4da0-a808-b443e9567036" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonStockSharesIssued_5a30836d-8233-422f-84d9-1effecb39c5c" xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_CommonStockSharesIssued"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_c0c423b2-ed24-4d49-bccd-0cf3d76c3416" xlink:to="loc_us-gaap_CommonStockSharesIssued_5a30836d-8233-422f-84d9-1effecb39c5c" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TreasuryStockShares_b21c40a2-5288-4a1e-a694-ba4d16a5ae50" xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_TreasuryStockShares"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_c0c423b2-ed24-4d49-bccd-0cf3d76c3416" xlink:to="loc_us-gaap_TreasuryStockShares_b21c40a2-5288-4a1e-a694-ba4d16a5ae50" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ProfitLoss_a2ebd032-6167-40ff-bea1-5972b033a26f" xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_ProfitLoss"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_c0c423b2-ed24-4d49-bccd-0cf3d76c3416" xlink:to="loc_us-gaap_ProfitLoss_a2ebd032-6167-40ff-bea1-5972b033a26f" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherComprehensiveIncomeLossNetOfTax_94b8ae58-3cc1-418c-a498-1d1b439bf844" xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_OtherComprehensiveIncomeLossNetOfTax"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_c0c423b2-ed24-4d49-bccd-0cf3d76c3416" xlink:to="loc_us-gaap_OtherComprehensiveIncomeLossNetOfTax_94b8ae58-3cc1-418c-a498-1d1b439bf844" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DividendsCommonStockCash_018b7819-6413-4d3a-9275-1d9d33125982" xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_DividendsCommonStockCash"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_c0c423b2-ed24-4d49-bccd-0cf3d76c3416" xlink:to="loc_us-gaap_DividendsCommonStockCash_018b7819-6413-4d3a-9275-1d9d33125982" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockIssuedDuringPeriodValueShareBasedCompensation_b5bb1c69-a04d-434c-8387-1a5953545a7f" xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_StockIssuedDuringPeriodValueShareBasedCompensation"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_c0c423b2-ed24-4d49-bccd-0cf3d76c3416" xlink:to="loc_us-gaap_StockIssuedDuringPeriodValueShareBasedCompensation_b5bb1c69-a04d-434c-8387-1a5953545a7f" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockIssuedDuringPeriodSharesShareBasedCompensation_a5716f31-d646-4052-9f8b-03b3151ccaed" xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_StockIssuedDuringPeriodSharesShareBasedCompensation"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_c0c423b2-ed24-4d49-bccd-0cf3d76c3416" xlink:to="loc_us-gaap_StockIssuedDuringPeriodSharesShareBasedCompensation_a5716f31-d646-4052-9f8b-03b3151ccaed" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AdjustmentsToAdditionalPaidInCapitalSharebasedCompensationRequisiteServicePeriodRecognitionValue_c5a5b0ba-b929-4f8a-9566-7821c75dadea" xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_AdjustmentsToAdditionalPaidInCapitalSharebasedCompensationRequisiteServicePeriodRecognitionValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_c0c423b2-ed24-4d49-bccd-0cf3d76c3416" xlink:to="loc_us-gaap_AdjustmentsToAdditionalPaidInCapitalSharebasedCompensationRequisiteServicePeriodRecognitionValue_c5a5b0ba-b929-4f8a-9566-7821c75dadea" xlink:type="arc" order="9"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ProceedsFromPaymentsToMinorityShareholders_31bda66d-e4e1-4acd-80b6-99e9467f6d6a" xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_ProceedsFromPaymentsToMinorityShareholders"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_c0c423b2-ed24-4d49-bccd-0cf3d76c3416" xlink:to="loc_us-gaap_ProceedsFromPaymentsToMinorityShareholders_31bda66d-e4e1-4acd-80b6-99e9467f6d6a" xlink:type="arc" order="10"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CumulativeEffectOnRetainedEarningsNetOfTax1_efab736f-673c-4b0c-8381-d62ebbcfe518" xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_CumulativeEffectOnRetainedEarningsNetOfTax1"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_c0c423b2-ed24-4d49-bccd-0cf3d76c3416" xlink:to="loc_us-gaap_CumulativeEffectOnRetainedEarningsNetOfTax1_efab736f-673c-4b0c-8381-d62ebbcfe518" xlink:type="arc" order="11"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockholdersEquityIncludingPortionAttributableToNoncontrollingInterest_9917209b-48c4-4f90-8c16-c46153e6463a" xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_StockholdersEquityIncludingPortionAttributableToNoncontrollingInterest"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonStockSharesIssued_96d0b700-3285-4ae4-a6ae-cc931da97c35" xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_CommonStockSharesIssued"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TreasuryStockShares_7c4646d7-c9f5-4a21-a3b2-f9e83bf641bd" xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_TreasuryStockShares"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementTable_06771bb7-f03e-487e-995c-b233829b2931" xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_StatementTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_StatementLineItems_ac96e3cf-5305-4a78-83a4-55f20c4bada4" xlink:to="loc_us-gaap_StatementTable_06771bb7-f03e-487e-995c-b233829b2931" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementEquityComponentsAxis_953d8456-0277-49cd-bfb4-a4926e0c71b6" xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_StatementEquityComponentsAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_StatementTable_06771bb7-f03e-487e-995c-b233829b2931" xlink:to="loc_us-gaap_StatementEquityComponentsAxis_953d8456-0277-49cd-bfb4-a4926e0c71b6" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EquityComponentDomain_953d8456-0277-49cd-bfb4-a4926e0c71b6_default" xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_EquityComponentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_StatementEquityComponentsAxis_953d8456-0277-49cd-bfb4-a4926e0c71b6" xlink:to="loc_us-gaap_EquityComponentDomain_953d8456-0277-49cd-bfb4-a4926e0c71b6_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EquityComponentDomain_a2fb1afb-78ea-43d8-afd1-2d05a0f52ce3" xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_EquityComponentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_StatementEquityComponentsAxis_953d8456-0277-49cd-bfb4-a4926e0c71b6" xlink:to="loc_us-gaap_EquityComponentDomain_a2fb1afb-78ea-43d8-afd1-2d05a0f52ce3" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonStockMember_7c828823-4475-4f1a-9f96-62f0880f9895" xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_CommonStockMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EquityComponentDomain_a2fb1afb-78ea-43d8-afd1-2d05a0f52ce3" xlink:to="loc_us-gaap_CommonStockMember_7c828823-4475-4f1a-9f96-62f0880f9895" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AdditionalPaidInCapitalMember_ee53e21f-35da-41e4-8813-240d3cdc3e76" xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_AdditionalPaidInCapitalMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EquityComponentDomain_a2fb1afb-78ea-43d8-afd1-2d05a0f52ce3" xlink:to="loc_us-gaap_AdditionalPaidInCapitalMember_ee53e21f-35da-41e4-8813-240d3cdc3e76" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AccumulatedOtherComprehensiveIncomeMember_bf999fc0-9ef5-4cd3-99cd-efe25c7f340e" xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_AccumulatedOtherComprehensiveIncomeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EquityComponentDomain_a2fb1afb-78ea-43d8-afd1-2d05a0f52ce3" xlink:to="loc_us-gaap_AccumulatedOtherComprehensiveIncomeMember_bf999fc0-9ef5-4cd3-99cd-efe25c7f340e" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RetainedEarningsMember_f08e89ba-1b9c-4c72-b1ed-3c5e0961110b" xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_RetainedEarningsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EquityComponentDomain_a2fb1afb-78ea-43d8-afd1-2d05a0f52ce3" xlink:to="loc_us-gaap_RetainedEarningsMember_f08e89ba-1b9c-4c72-b1ed-3c5e0961110b" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TreasuryStockMember_b8dfd26b-2b3f-4bfd-81c0-ee02c38404d5" xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_TreasuryStockMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EquityComponentDomain_a2fb1afb-78ea-43d8-afd1-2d05a0f52ce3" xlink:to="loc_us-gaap_TreasuryStockMember_b8dfd26b-2b3f-4bfd-81c0-ee02c38404d5" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NoncontrollingInterestMember_fe792751-e253-414f-944a-3242ef43abb1" xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_NoncontrollingInterestMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EquityComponentDomain_a2fb1afb-78ea-43d8-afd1-2d05a0f52ce3" xlink:to="loc_us-gaap_NoncontrollingInterestMember_fe792751-e253-414f-944a-3242ef43abb1" xlink:type="arc" order="5"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.cmc.com/role/CONDENSEDCONSOLIDATEDSTATEMENTSOFSTOCKHOLDERSEQUITYUNAUDITEDParenthetical" xlink:type="simple" xlink:href="cmc-20200229.xsd#CONDENSEDCONSOLIDATEDSTATEMENTSOFSTOCKHOLDERSEQUITYUNAUDITEDParenthetical"/>
  <link:definitionLink xlink:role="http://www.cmc.com/role/CONDENSEDCONSOLIDATEDSTATEMENTSOFSTOCKHOLDERSEQUITYUNAUDITEDParenthetical" xlink:type="extended" id="ifebe2c27c2764f558589aff579dba378_80ed7f22-d53b-4ed2-a859-997eed1943b7"/>
  <link:roleRef roleURI="http://www.cmc.com/role/ACCOUNTINGPOLICIES" xlink:type="simple" xlink:href="cmc-20200229.xsd#ACCOUNTINGPOLICIES"/>
  <link:definitionLink xlink:role="http://www.cmc.com/role/ACCOUNTINGPOLICIES" xlink:type="extended" id="i83d22a2606114f3bb752a24d817290ac_260d3f5e-28c8-458a-8edf-7066c0e85375"/>
  <link:roleRef roleURI="http://www.cmc.com/role/ACCOUNTINGPOLICIESPolicies" xlink:type="simple" xlink:href="cmc-20200229.xsd#ACCOUNTINGPOLICIESPolicies"/>
  <link:definitionLink xlink:role="http://www.cmc.com/role/ACCOUNTINGPOLICIESPolicies" xlink:type="extended" id="ic7e431d74e8e45cba3c93823137d4be1_fe2225c1-41a3-4949-af0c-e4d21df30127"/>
  <link:roleRef roleURI="http://www.cmc.com/role/ACCOUNTINGPOLICIESRecentlyAdoptedAccountingPronouncementsDetails" xlink:type="simple" xlink:href="cmc-20200229.xsd#ACCOUNTINGPOLICIESRecentlyAdoptedAccountingPronouncementsDetails"/>
  <link:definitionLink xlink:role="http://www.cmc.com/role/ACCOUNTINGPOLICIESRecentlyAdoptedAccountingPronouncementsDetails" xlink:type="extended" id="i26d01667cf3b454fba1643cf53ba74d4_66a31c45-f46c-45c4-bd9c-eea5f959e2fb">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NewAccountingPronouncementsOrChangeInAccountingPrincipleLineItems_b2d4a02f-2acd-4a9c-9d7f-fe2c06cdcea0" xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_NewAccountingPronouncementsOrChangeInAccountingPrincipleLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OperatingLeaseRightOfUseAsset_3fba7594-4b3f-4198-9eaa-0157cfe7d249" xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_OperatingLeaseRightOfUseAsset"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_NewAccountingPronouncementsOrChangeInAccountingPrincipleLineItems_b2d4a02f-2acd-4a9c-9d7f-fe2c06cdcea0" xlink:to="loc_us-gaap_OperatingLeaseRightOfUseAsset_3fba7594-4b3f-4198-9eaa-0157cfe7d249" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OperatingLeaseLiabilityCurrent_3215140c-f648-4ed2-b494-be3485912400" xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_OperatingLeaseLiabilityCurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_NewAccountingPronouncementsOrChangeInAccountingPrincipleLineItems_b2d4a02f-2acd-4a9c-9d7f-fe2c06cdcea0" xlink:to="loc_us-gaap_OperatingLeaseLiabilityCurrent_3215140c-f648-4ed2-b494-be3485912400" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OperatingLeaseLiabilityNoncurrent_3d3cefce-5892-41fe-84db-4001bb91369e" xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_OperatingLeaseLiabilityNoncurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_NewAccountingPronouncementsOrChangeInAccountingPrincipleLineItems_b2d4a02f-2acd-4a9c-9d7f-fe2c06cdcea0" xlink:to="loc_us-gaap_OperatingLeaseLiabilityNoncurrent_3d3cefce-5892-41fe-84db-4001bb91369e" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CumulativeEffectOnRetainedEarningsNetOfTax1_6b1efb4f-f46d-4186-b2be-0a906d14458a" xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_CumulativeEffectOnRetainedEarningsNetOfTax1"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_NewAccountingPronouncementsOrChangeInAccountingPrincipleLineItems_b2d4a02f-2acd-4a9c-9d7f-fe2c06cdcea0" xlink:to="loc_us-gaap_CumulativeEffectOnRetainedEarningsNetOfTax1_6b1efb4f-f46d-4186-b2be-0a906d14458a" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NewAccountingPronouncementsOrChangeInAccountingPrincipleTable_59129b9d-8640-4262-9e5d-d990cf162f68" xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_NewAccountingPronouncementsOrChangeInAccountingPrincipleTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_NewAccountingPronouncementsOrChangeInAccountingPrincipleLineItems_b2d4a02f-2acd-4a9c-9d7f-fe2c06cdcea0" xlink:to="loc_us-gaap_NewAccountingPronouncementsOrChangeInAccountingPrincipleTable_59129b9d-8640-4262-9e5d-d990cf162f68" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BalanceSheetLocationAxis_340afe60-7734-4588-a1ef-cce995d9f69a" xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_BalanceSheetLocationAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_NewAccountingPronouncementsOrChangeInAccountingPrincipleTable_59129b9d-8640-4262-9e5d-d990cf162f68" xlink:to="loc_us-gaap_BalanceSheetLocationAxis_340afe60-7734-4588-a1ef-cce995d9f69a" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BalanceSheetLocationDomain_340afe60-7734-4588-a1ef-cce995d9f69a_default" xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_BalanceSheetLocationDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_BalanceSheetLocationAxis_340afe60-7734-4588-a1ef-cce995d9f69a" xlink:to="loc_us-gaap_BalanceSheetLocationDomain_340afe60-7734-4588-a1ef-cce995d9f69a_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BalanceSheetLocationDomain_2deb63eb-3765-4e39-a928-43af487c1d21" xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_BalanceSheetLocationDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_BalanceSheetLocationAxis_340afe60-7734-4588-a1ef-cce995d9f69a" xlink:to="loc_us-gaap_BalanceSheetLocationDomain_2deb63eb-3765-4e39-a928-43af487c1d21" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherNoncurrentAssetsMember_30b9434f-27e0-4f29-9018-f30cbe7a135d" xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_OtherNoncurrentAssetsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BalanceSheetLocationDomain_2deb63eb-3765-4e39-a928-43af487c1d21" xlink:to="loc_us-gaap_OtherNoncurrentAssetsMember_30b9434f-27e0-4f29-9018-f30cbe7a135d" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_cmc_AccruedExpensesandOtherPayablesMember_99432f10-df86-4646-8d63-706e90dbc36e" xlink:href="cmc-20200229.xsd#cmc_AccruedExpensesandOtherPayablesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BalanceSheetLocationDomain_2deb63eb-3765-4e39-a928-43af487c1d21" xlink:to="loc_cmc_AccruedExpensesandOtherPayablesMember_99432f10-df86-4646-8d63-706e90dbc36e" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherNoncurrentLiabilitiesMember_e68909a4-46f3-4dd9-894b-5bad96ad9b8a" xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_OtherNoncurrentLiabilitiesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BalanceSheetLocationDomain_2deb63eb-3765-4e39-a928-43af487c1d21" xlink:to="loc_us-gaap_OtherNoncurrentLiabilitiesMember_e68909a4-46f3-4dd9-894b-5bad96ad9b8a" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AdjustmentsForNewAccountingPronouncementsAxis_fe4d7c7b-5a03-4ce6-a26c-ce64da45bca0" xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_AdjustmentsForNewAccountingPronouncementsAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_NewAccountingPronouncementsOrChangeInAccountingPrincipleTable_59129b9d-8640-4262-9e5d-d990cf162f68" xlink:to="loc_us-gaap_AdjustmentsForNewAccountingPronouncementsAxis_fe4d7c7b-5a03-4ce6-a26c-ce64da45bca0" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TypeOfAdoptionMember_fe4d7c7b-5a03-4ce6-a26c-ce64da45bca0_default" xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_TypeOfAdoptionMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_AdjustmentsForNewAccountingPronouncementsAxis_fe4d7c7b-5a03-4ce6-a26c-ce64da45bca0" xlink:to="loc_us-gaap_TypeOfAdoptionMember_fe4d7c7b-5a03-4ce6-a26c-ce64da45bca0_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TypeOfAdoptionMember_77a77eb5-0bdf-4261-b989-e2885e9afa47" xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_TypeOfAdoptionMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_AdjustmentsForNewAccountingPronouncementsAxis_fe4d7c7b-5a03-4ce6-a26c-ce64da45bca0" xlink:to="loc_us-gaap_TypeOfAdoptionMember_77a77eb5-0bdf-4261-b989-e2885e9afa47" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AccountingStandardsUpdate201602Member_674e37dd-b7fe-4415-8ce9-8a93fe5df3cc" xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_AccountingStandardsUpdate201602Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_TypeOfAdoptionMember_77a77eb5-0bdf-4261-b989-e2885e9afa47" xlink:to="loc_us-gaap_AccountingStandardsUpdate201602Member_674e37dd-b7fe-4415-8ce9-8a93fe5df3cc" xlink:type="arc" order="0"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.cmc.com/role/CHANGESINBUSINESS" xlink:type="simple" xlink:href="cmc-20200229.xsd#CHANGESINBUSINESS"/>
  <link:definitionLink xlink:role="http://www.cmc.com/role/CHANGESINBUSINESS" xlink:type="extended" id="ibb89e30850d1459a9f1d101b4f9ee88d_f6d8298d-027e-4c10-b42c-f6d13c2b7767"/>
  <link:roleRef roleURI="http://www.cmc.com/role/CHANGESINBUSINESSTables" xlink:type="simple" xlink:href="cmc-20200229.xsd#CHANGESINBUSINESSTables"/>
  <link:definitionLink xlink:role="http://www.cmc.com/role/CHANGESINBUSINESSTables" xlink:type="extended" id="ia8bbb4e92b3744db8d84c7796ccacf9b_530a823e-3f0f-4db1-8a0e-18529c744221"/>
  <link:roleRef roleURI="http://www.cmc.com/role/CHANGESINBUSINESSDetails" xlink:type="simple" xlink:href="cmc-20200229.xsd#CHANGESINBUSINESSDetails"/>
  <link:definitionLink xlink:role="http://www.cmc.com/role/CHANGESINBUSINESSDetails" xlink:type="extended" id="i30cd09004d3141c5bd21c1b3a256577b_153577d0-19d1-4b5d-8637-59853282d800"/>
  <link:roleRef roleURI="http://www.cmc.com/role/ACCUMULATEDOTHERCOMPREHENSIVEINCOMELOSS" xlink:type="simple" xlink:href="cmc-20200229.xsd#ACCUMULATEDOTHERCOMPREHENSIVEINCOMELOSS"/>
  <link:definitionLink xlink:role="http://www.cmc.com/role/ACCUMULATEDOTHERCOMPREHENSIVEINCOMELOSS" xlink:type="extended" id="i7b789e6537c84e54ba3a2a941f32a968_94d40cd7-6486-423a-aa05-db9cb3eae57d"/>
  <link:roleRef roleURI="http://www.cmc.com/role/ACCUMULATEDOTHERCOMPREHENSIVEINCOMELOSSTables" xlink:type="simple" xlink:href="cmc-20200229.xsd#ACCUMULATEDOTHERCOMPREHENSIVEINCOMELOSSTables"/>
  <link:definitionLink xlink:role="http://www.cmc.com/role/ACCUMULATEDOTHERCOMPREHENSIVEINCOMELOSSTables" xlink:type="extended" id="ifba85e6db51b469982c48e9197fa688e_164eed10-45f5-43d7-96c5-6db3d8af8a44"/>
  <link:roleRef roleURI="http://www.cmc.com/role/ACCUMULATEDOTHERCOMPREHENSIVEINCOMELOSSAOCIbyComponentsDetails" xlink:type="simple" xlink:href="cmc-20200229.xsd#ACCUMULATEDOTHERCOMPREHENSIVEINCOMELOSSAOCIbyComponentsDetails"/>
  <link:definitionLink xlink:role="http://www.cmc.com/role/ACCUMULATEDOTHERCOMPREHENSIVEINCOMELOSSAOCIbyComponentsDetails" xlink:type="extended" id="iad78282fc7ed4116acdccf29956ad5d0_dd07a23a-3334-427a-8de4-9581db8872eb">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AccumulatedOtherComprehensiveIncomeLossLineItems_4db55abb-ce4a-42e0-987b-74863ab2a02e" xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_AccumulatedOtherComprehensiveIncomeLossLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AOCIAttributableToParentNetOfTaxRollForward_25aa783e-f7d2-409b-a167-03b8519df295" xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_AOCIAttributableToParentNetOfTaxRollForward"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AccumulatedOtherComprehensiveIncomeLossLineItems_4db55abb-ce4a-42e0-987b-74863ab2a02e" xlink:to="loc_us-gaap_AOCIAttributableToParentNetOfTaxRollForward_25aa783e-f7d2-409b-a167-03b8519df295" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AccumulatedOtherComprehensiveIncomeLossNetOfTax_0c2218db-428c-4b56-9460-fb1679985e0f" xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_AccumulatedOtherComprehensiveIncomeLossNetOfTax"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AOCIAttributableToParentNetOfTaxRollForward_25aa783e-f7d2-409b-a167-03b8519df295" xlink:to="loc_us-gaap_AccumulatedOtherComprehensiveIncomeLossNetOfTax_0c2218db-428c-4b56-9460-fb1679985e0f" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherComprehensiveIncomeLossBeforeReclassificationsBeforeTax_aad1f65f-7bac-495f-99c4-9968ed4aaa56" xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_OtherComprehensiveIncomeLossBeforeReclassificationsBeforeTax"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AOCIAttributableToParentNetOfTaxRollForward_25aa783e-f7d2-409b-a167-03b8519df295" xlink:to="loc_us-gaap_OtherComprehensiveIncomeLossBeforeReclassificationsBeforeTax_aad1f65f-7bac-495f-99c4-9968ed4aaa56" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ReclassificationFromAccumulatedOtherComprehensiveIncomeCurrentPeriodBeforeTax_a8470098-52f0-46aa-855d-95e1af0e27bc" xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_ReclassificationFromAccumulatedOtherComprehensiveIncomeCurrentPeriodBeforeTax"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AOCIAttributableToParentNetOfTaxRollForward_25aa783e-f7d2-409b-a167-03b8519df295" xlink:to="loc_us-gaap_ReclassificationFromAccumulatedOtherComprehensiveIncomeCurrentPeriodBeforeTax_a8470098-52f0-46aa-855d-95e1af0e27bc" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherComprehensiveIncomeLossTax_ebdca739-b543-445f-ad10-56fa3a947b9d" xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_OtherComprehensiveIncomeLossTax"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AOCIAttributableToParentNetOfTaxRollForward_25aa783e-f7d2-409b-a167-03b8519df295" xlink:to="loc_us-gaap_OtherComprehensiveIncomeLossTax_ebdca739-b543-445f-ad10-56fa3a947b9d" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherComprehensiveIncomeLossNetOfTax_7115e5e8-b67c-4d37-b88e-4800fd6f5be7" xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_OtherComprehensiveIncomeLossNetOfTax"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AOCIAttributableToParentNetOfTaxRollForward_25aa783e-f7d2-409b-a167-03b8519df295" xlink:to="loc_us-gaap_OtherComprehensiveIncomeLossNetOfTax_7115e5e8-b67c-4d37-b88e-4800fd6f5be7" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AccumulatedOtherComprehensiveIncomeLossNetOfTax_304dd8ca-d099-441f-b2d3-e99010230f0c" xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_AccumulatedOtherComprehensiveIncomeLossNetOfTax"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AccumulatedOtherComprehensiveIncomeLossTable_d686506a-070b-4fa2-bd1c-7e1477d2fc26" xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_AccumulatedOtherComprehensiveIncomeLossTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_AccumulatedOtherComprehensiveIncomeLossLineItems_4db55abb-ce4a-42e0-987b-74863ab2a02e" xlink:to="loc_us-gaap_AccumulatedOtherComprehensiveIncomeLossTable_d686506a-070b-4fa2-bd1c-7e1477d2fc26" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementEquityComponentsAxis_839196ee-661c-4c71-9791-ea95649cae6d" xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_StatementEquityComponentsAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_AccumulatedOtherComprehensiveIncomeLossTable_d686506a-070b-4fa2-bd1c-7e1477d2fc26" xlink:to="loc_us-gaap_StatementEquityComponentsAxis_839196ee-661c-4c71-9791-ea95649cae6d" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EquityComponentDomain_839196ee-661c-4c71-9791-ea95649cae6d_default" xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_EquityComponentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_StatementEquityComponentsAxis_839196ee-661c-4c71-9791-ea95649cae6d" xlink:to="loc_us-gaap_EquityComponentDomain_839196ee-661c-4c71-9791-ea95649cae6d_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EquityComponentDomain_74e65dee-6b19-46a3-be44-ddad66eb5dc9" xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_EquityComponentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_StatementEquityComponentsAxis_839196ee-661c-4c71-9791-ea95649cae6d" xlink:to="loc_us-gaap_EquityComponentDomain_74e65dee-6b19-46a3-be44-ddad66eb5dc9" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AccumulatedTranslationAdjustmentMember_563d6a0e-57cb-45b9-ad69-d22fd1d887be" xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_AccumulatedTranslationAdjustmentMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EquityComponentDomain_74e65dee-6b19-46a3-be44-ddad66eb5dc9" xlink:to="loc_us-gaap_AccumulatedTranslationAdjustmentMember_563d6a0e-57cb-45b9-ad69-d22fd1d887be" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AccumulatedNetGainLossFromDesignatedOrQualifyingCashFlowHedgesMember_c837b92e-c489-4f91-9062-6dc762d65f6b" xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_AccumulatedNetGainLossFromDesignatedOrQualifyingCashFlowHedgesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EquityComponentDomain_74e65dee-6b19-46a3-be44-ddad66eb5dc9" xlink:to="loc_us-gaap_AccumulatedNetGainLossFromDesignatedOrQualifyingCashFlowHedgesMember_c837b92e-c489-4f91-9062-6dc762d65f6b" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AccumulatedDefinedBenefitPlansAdjustmentMember_c622a373-50ab-4433-a2e4-17c64c5c1443" xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_AccumulatedDefinedBenefitPlansAdjustmentMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EquityComponentDomain_74e65dee-6b19-46a3-be44-ddad66eb5dc9" xlink:to="loc_us-gaap_AccumulatedDefinedBenefitPlansAdjustmentMember_c622a373-50ab-4433-a2e4-17c64c5c1443" xlink:type="arc" order="2"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.cmc.com/role/REVENUERECOGNITION" xlink:type="simple" xlink:href="cmc-20200229.xsd#REVENUERECOGNITION"/>
  <link:definitionLink xlink:role="http://www.cmc.com/role/REVENUERECOGNITION" xlink:type="extended" id="ie273667f2ba24fa89c49c1607d512104_7d7832a7-9fb5-483e-b6bb-f4f482ba3ab7"/>
  <link:roleRef roleURI="http://www.cmc.com/role/REVENUERECOGNITIONTables" xlink:type="simple" xlink:href="cmc-20200229.xsd#REVENUERECOGNITIONTables"/>
  <link:definitionLink xlink:role="http://www.cmc.com/role/REVENUERECOGNITIONTables" xlink:type="extended" id="i3f50bdff9ff64f998ea3033d434588ea_6b382569-a2a0-4260-b1b9-7e18b6c44abf"/>
  <link:roleRef roleURI="http://www.cmc.com/role/REVENUERECOGNITIONRevenueRecognitionMethodDetails" xlink:type="simple" xlink:href="cmc-20200229.xsd#REVENUERECOGNITIONRevenueRecognitionMethodDetails"/>
  <link:definitionLink xlink:role="http://www.cmc.com/role/REVENUERECOGNITIONRevenueRecognitionMethodDetails" xlink:type="extended" id="i1cab296076534c228853f50b304fa1a7_b63fb044-364b-4bda-b891-3176865d286c">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DisaggregationOfRevenueLineItems_125fef3b-525d-4a0b-9adb-2bc5220d9cdc" xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_DisaggregationOfRevenueLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_cmc_ContractwithCustomerContractasPercentofTotalRevenue_c6d0f000-e593-418f-b3ea-936cdfe07fc9" xlink:href="cmc-20200229.xsd#cmc_ContractwithCustomerContractasPercentofTotalRevenue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DisaggregationOfRevenueLineItems_125fef3b-525d-4a0b-9adb-2bc5220d9cdc" xlink:to="loc_cmc_ContractwithCustomerContractasPercentofTotalRevenue_c6d0f000-e593-418f-b3ea-936cdfe07fc9" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DisaggregationOfRevenueTable_f6d6d507-a548-409f-9c7d-2833177dd643" xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_DisaggregationOfRevenueTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_DisaggregationOfRevenueLineItems_125fef3b-525d-4a0b-9adb-2bc5220d9cdc" xlink:to="loc_us-gaap_DisaggregationOfRevenueTable_f6d6d507-a548-409f-9c7d-2833177dd643" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementBusinessSegmentsAxis_3a259115-a053-489d-a463-f48be05d699c" xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_StatementBusinessSegmentsAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DisaggregationOfRevenueTable_f6d6d507-a548-409f-9c7d-2833177dd643" xlink:to="loc_us-gaap_StatementBusinessSegmentsAxis_3a259115-a053-489d-a463-f48be05d699c" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SegmentDomain_3a259115-a053-489d-a463-f48be05d699c_default" xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_SegmentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_StatementBusinessSegmentsAxis_3a259115-a053-489d-a463-f48be05d699c" xlink:to="loc_us-gaap_SegmentDomain_3a259115-a053-489d-a463-f48be05d699c_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SegmentDomain_b30cdc66-b7de-4de2-9332-597b499e3594" xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_SegmentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_StatementBusinessSegmentsAxis_3a259115-a053-489d-a463-f48be05d699c" xlink:to="loc_us-gaap_SegmentDomain_b30cdc66-b7de-4de2-9332-597b499e3594" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_cmc_AmericasFabricationMember_8615f8f7-95af-4fd4-a7be-6ef13e64c929" xlink:href="cmc-20200229.xsd#cmc_AmericasFabricationMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentDomain_b30cdc66-b7de-4de2-9332-597b499e3594" xlink:to="loc_cmc_AmericasFabricationMember_8615f8f7-95af-4fd4-a7be-6ef13e64c929" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ProductOrServiceAxis_d94a0662-8cde-415b-b7ab-d717cb8d9b33" xlink:href="http://xbrl.fasb.org/srt/2019/elts/srt-2019-01-31.xsd#srt_ProductOrServiceAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DisaggregationOfRevenueTable_f6d6d507-a548-409f-9c7d-2833177dd643" xlink:to="loc_srt_ProductOrServiceAxis_d94a0662-8cde-415b-b7ab-d717cb8d9b33" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ProductsAndServicesDomain_d94a0662-8cde-415b-b7ab-d717cb8d9b33_default" xlink:href="http://xbrl.fasb.org/srt/2019/elts/srt-2019-01-31.xsd#srt_ProductsAndServicesDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_ProductOrServiceAxis_d94a0662-8cde-415b-b7ab-d717cb8d9b33" xlink:to="loc_srt_ProductsAndServicesDomain_d94a0662-8cde-415b-b7ab-d717cb8d9b33_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ProductsAndServicesDomain_931d110d-7cd8-41ee-89e3-b28bffe96b37" xlink:href="http://xbrl.fasb.org/srt/2019/elts/srt-2019-01-31.xsd#srt_ProductsAndServicesDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_ProductOrServiceAxis_d94a0662-8cde-415b-b7ab-d717cb8d9b33" xlink:to="loc_srt_ProductsAndServicesDomain_931d110d-7cd8-41ee-89e3-b28bffe96b37" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_cmc_FabricatedProductandInstallationServicesMember_139beebc-7f07-4d44-ab17-33063eb9f3b4" xlink:href="cmc-20200229.xsd#cmc_FabricatedProductandInstallationServicesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ProductsAndServicesDomain_931d110d-7cd8-41ee-89e3-b28bffe96b37" xlink:to="loc_cmc_FabricatedProductandInstallationServicesMember_139beebc-7f07-4d44-ab17-33063eb9f3b4" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_cmc_FabricatedProductwithoutInstallationServicesMember_e15cf0cd-20ca-4d85-a2cc-125b60832149" xlink:href="cmc-20200229.xsd#cmc_FabricatedProductwithoutInstallationServicesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ProductsAndServicesDomain_931d110d-7cd8-41ee-89e3-b28bffe96b37" xlink:to="loc_cmc_FabricatedProductwithoutInstallationServicesMember_e15cf0cd-20ca-4d85-a2cc-125b60832149" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TimingOfTransferOfGoodOrServiceAxis_5741ba48-ea2c-433f-9c2b-d1b88d68ec24" xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_TimingOfTransferOfGoodOrServiceAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DisaggregationOfRevenueTable_f6d6d507-a548-409f-9c7d-2833177dd643" xlink:to="loc_us-gaap_TimingOfTransferOfGoodOrServiceAxis_5741ba48-ea2c-433f-9c2b-d1b88d68ec24" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TimingOfTransferOfGoodOrServiceDomain_5741ba48-ea2c-433f-9c2b-d1b88d68ec24_default" xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_TimingOfTransferOfGoodOrServiceDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_TimingOfTransferOfGoodOrServiceAxis_5741ba48-ea2c-433f-9c2b-d1b88d68ec24" xlink:to="loc_us-gaap_TimingOfTransferOfGoodOrServiceDomain_5741ba48-ea2c-433f-9c2b-d1b88d68ec24_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TimingOfTransferOfGoodOrServiceDomain_b0583075-d8e0-408b-80b2-151de94e5e59" xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_TimingOfTransferOfGoodOrServiceDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_TimingOfTransferOfGoodOrServiceAxis_5741ba48-ea2c-433f-9c2b-d1b88d68ec24" xlink:to="loc_us-gaap_TimingOfTransferOfGoodOrServiceDomain_b0583075-d8e0-408b-80b2-151de94e5e59" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TransferredOverTimeMember_9d44546a-5d63-4e58-a971-8ab97fe6b698" xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_TransferredOverTimeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_TimingOfTransferOfGoodOrServiceDomain_b0583075-d8e0-408b-80b2-151de94e5e59" xlink:to="loc_us-gaap_TransferredOverTimeMember_9d44546a-5d63-4e58-a971-8ab97fe6b698" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TransferredAtPointInTimeMember_c7f84d1b-5b80-48eb-8596-d5f4af431bce" xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_TransferredAtPointInTimeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_TimingOfTransferOfGoodOrServiceDomain_b0583075-d8e0-408b-80b2-151de94e5e59" xlink:to="loc_us-gaap_TransferredAtPointInTimeMember_c7f84d1b-5b80-48eb-8596-d5f4af431bce" xlink:type="arc" order="1"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.cmc.com/role/REVENUERECOGNITIONContractAssetsandContractLiabilitiesDetails" xlink:type="simple" xlink:href="cmc-20200229.xsd#REVENUERECOGNITIONContractAssetsandContractLiabilitiesDetails"/>
  <link:definitionLink xlink:role="http://www.cmc.com/role/REVENUERECOGNITIONContractAssetsandContractLiabilitiesDetails" xlink:type="extended" id="i6bc5598d365d4d909547e753d6b6624d_e5bd8999-649c-4b9b-b2ca-a8712c9fad06"/>
  <link:roleRef roleURI="http://www.cmc.com/role/REVENUERECOGNITIONRemainingPerformanceObligationsDetails" xlink:type="simple" xlink:href="cmc-20200229.xsd#REVENUERECOGNITIONRemainingPerformanceObligationsDetails"/>
  <link:definitionLink xlink:role="http://www.cmc.com/role/REVENUERECOGNITIONRemainingPerformanceObligationsDetails" xlink:type="extended" id="i42db8ea30b954bfdb5a00090e19edbf9_8f75ba61-85bf-4db7-a0c8-3195151df4fd">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionLineItems_ca49ead3-ae5e-4325-9925-ab044df51fbe" xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RevenueRemainingPerformanceObligation_ecd64444-5458-49e8-a4d2-9d320c035afc" xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_RevenueRemainingPerformanceObligation"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionLineItems_ca49ead3-ae5e-4325-9925-ab044df51fbe" xlink:to="loc_us-gaap_RevenueRemainingPerformanceObligation_ecd64444-5458-49e8-a4d2-9d320c035afc" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RevenueRemainingPerformanceObligationPercentage_70b7a9ea-4d28-476a-8216-25b5455b61d3" xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_RevenueRemainingPerformanceObligationPercentage"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionLineItems_ca49ead3-ae5e-4325-9925-ab044df51fbe" xlink:to="loc_us-gaap_RevenueRemainingPerformanceObligationPercentage_70b7a9ea-4d28-476a-8216-25b5455b61d3" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionPeriod1_f6c28870-a482-4223-94f0-91c8b9297d40" xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionPeriod1"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionLineItems_ca49ead3-ae5e-4325-9925-ab044df51fbe" xlink:to="loc_us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionPeriod1_f6c28870-a482-4223-94f0-91c8b9297d40" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionTable_11a6924f-081b-46b4-a732-1e6b18efb181" xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionLineItems_ca49ead3-ae5e-4325-9925-ab044df51fbe" xlink:to="loc_us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionTable_11a6924f-081b-46b4-a732-1e6b18efb181" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionStartDateAxis_f09d55eb-9a78-4290-b6aa-08fd92ffe0e2" xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionStartDateAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionTable_11a6924f-081b-46b4-a732-1e6b18efb181" xlink:to="loc_us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionStartDateAxis_f09d55eb-9a78-4290-b6aa-08fd92ffe0e2" xlink:type="arc" order="1"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.cmc.com/role/REVENUERECOGNITIONRemainingPerformanceObligationsDetailsDefault" xlink:type="simple" xlink:href="cmc-20200229.xsd#REVENUERECOGNITIONRemainingPerformanceObligationsDetailsDefault"/>
  <link:definitionLink xlink:role="http://www.cmc.com/role/REVENUERECOGNITIONRemainingPerformanceObligationsDetailsDefault" xlink:type="extended" id="i736df1679c8749bcbd8ce077db9796af_8f75ba61-85bf-4db7-a0c8-3195151df4fdDefault">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionLineItems_ca49ead3-ae5e-4325-9925-ab044df51fbe" xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RevenueRemainingPerformanceObligation_ecd64444-5458-49e8-a4d2-9d320c035afc" xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_RevenueRemainingPerformanceObligation"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionLineItems_ca49ead3-ae5e-4325-9925-ab044df51fbe" xlink:to="loc_us-gaap_RevenueRemainingPerformanceObligation_ecd64444-5458-49e8-a4d2-9d320c035afc" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RevenueRemainingPerformanceObligationPercentage_70b7a9ea-4d28-476a-8216-25b5455b61d3" xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_RevenueRemainingPerformanceObligationPercentage"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionLineItems_ca49ead3-ae5e-4325-9925-ab044df51fbe" xlink:to="loc_us-gaap_RevenueRemainingPerformanceObligationPercentage_70b7a9ea-4d28-476a-8216-25b5455b61d3" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionPeriod1_f6c28870-a482-4223-94f0-91c8b9297d40" xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionPeriod1"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionLineItems_ca49ead3-ae5e-4325-9925-ab044df51fbe" xlink:to="loc_us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionPeriod1_f6c28870-a482-4223-94f0-91c8b9297d40" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionTable_11a6924f-081b-46b4-a732-1e6b18efb181" xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionLineItems_ca49ead3-ae5e-4325-9925-ab044df51fbe" xlink:to="loc_us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionTable_11a6924f-081b-46b4-a732-1e6b18efb181" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.cmc.com/role/REVENUERECOGNITIONDisaggregationofRevenueDetails" xlink:type="simple" xlink:href="cmc-20200229.xsd#REVENUERECOGNITIONDisaggregationofRevenueDetails"/>
  <link:definitionLink xlink:role="http://www.cmc.com/role/REVENUERECOGNITIONDisaggregationofRevenueDetails" xlink:type="extended" id="i6096d6faad7e4aafaf11adbada8814ac_7d5c0f5f-624d-4540-9694-bfec803e0534">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DisaggregationOfRevenueLineItems_bb3452cf-ce4e-4041-80e1-d09ae1b7a073" xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_DisaggregationOfRevenueLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RevenueFromContractWithCustomerIncludingAssessedTax_6b3b9c51-3487-4eda-8e11-ed057ecb47c4" xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_RevenueFromContractWithCustomerIncludingAssessedTax"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DisaggregationOfRevenueLineItems_bb3452cf-ce4e-4041-80e1-d09ae1b7a073" xlink:to="loc_us-gaap_RevenueFromContractWithCustomerIncludingAssessedTax_6b3b9c51-3487-4eda-8e11-ed057ecb47c4" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DisaggregationOfRevenueTable_75ce87f4-45fa-4613-a55c-426cd39a3e55" xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_DisaggregationOfRevenueTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_DisaggregationOfRevenueLineItems_bb3452cf-ce4e-4041-80e1-d09ae1b7a073" xlink:to="loc_us-gaap_DisaggregationOfRevenueTable_75ce87f4-45fa-4613-a55c-426cd39a3e55" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementBusinessSegmentsAxis_317d77f6-4539-4c1c-8a66-74ac30681646" xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_StatementBusinessSegmentsAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DisaggregationOfRevenueTable_75ce87f4-45fa-4613-a55c-426cd39a3e55" xlink:to="loc_us-gaap_StatementBusinessSegmentsAxis_317d77f6-4539-4c1c-8a66-74ac30681646" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SegmentDomain_317d77f6-4539-4c1c-8a66-74ac30681646_default" xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_SegmentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_StatementBusinessSegmentsAxis_317d77f6-4539-4c1c-8a66-74ac30681646" xlink:to="loc_us-gaap_SegmentDomain_317d77f6-4539-4c1c-8a66-74ac30681646_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SegmentDomain_8dde9f9e-1270-44c6-9c24-b5d38a2ce002" xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_SegmentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_StatementBusinessSegmentsAxis_317d77f6-4539-4c1c-8a66-74ac30681646" xlink:to="loc_us-gaap_SegmentDomain_8dde9f9e-1270-44c6-9c24-b5d38a2ce002" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_cmc_AmericasRecyclingMember_217c2059-1d8d-4933-b409-2d8d0189c53a" xlink:href="cmc-20200229.xsd#cmc_AmericasRecyclingMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentDomain_8dde9f9e-1270-44c6-9c24-b5d38a2ce002" xlink:to="loc_cmc_AmericasRecyclingMember_217c2059-1d8d-4933-b409-2d8d0189c53a" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_cmc_AmericasMillsMember_ceddcc39-684d-4405-9d99-4e312be664e5" xlink:href="cmc-20200229.xsd#cmc_AmericasMillsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentDomain_8dde9f9e-1270-44c6-9c24-b5d38a2ce002" xlink:to="loc_cmc_AmericasMillsMember_ceddcc39-684d-4405-9d99-4e312be664e5" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_cmc_AmericasFabricationMember_581d57e1-3f5d-476a-b4b6-7e79923b5c10" xlink:href="cmc-20200229.xsd#cmc_AmericasFabricationMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentDomain_8dde9f9e-1270-44c6-9c24-b5d38a2ce002" xlink:to="loc_cmc_AmericasFabricationMember_581d57e1-3f5d-476a-b4b6-7e79923b5c10" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_cmc_InternationalMillsMember_894f10c3-975a-46f8-ae24-28b5070af6ed" xlink:href="cmc-20200229.xsd#cmc_InternationalMillsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentDomain_8dde9f9e-1270-44c6-9c24-b5d38a2ce002" xlink:to="loc_cmc_InternationalMillsMember_894f10c3-975a-46f8-ae24-28b5070af6ed" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CorporateMember_77a3e2c8-e703-4d96-a9d1-49e1f827d654" xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_CorporateMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentDomain_8dde9f9e-1270-44c6-9c24-b5d38a2ce002" xlink:to="loc_us-gaap_CorporateMember_77a3e2c8-e703-4d96-a9d1-49e1f827d654" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ProductOrServiceAxis_1501ff26-b142-49ec-a63c-2fb449a118f3" xlink:href="http://xbrl.fasb.org/srt/2019/elts/srt-2019-01-31.xsd#srt_ProductOrServiceAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DisaggregationOfRevenueTable_75ce87f4-45fa-4613-a55c-426cd39a3e55" xlink:to="loc_srt_ProductOrServiceAxis_1501ff26-b142-49ec-a63c-2fb449a118f3" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ProductsAndServicesDomain_1501ff26-b142-49ec-a63c-2fb449a118f3_default" xlink:href="http://xbrl.fasb.org/srt/2019/elts/srt-2019-01-31.xsd#srt_ProductsAndServicesDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_ProductOrServiceAxis_1501ff26-b142-49ec-a63c-2fb449a118f3" xlink:to="loc_srt_ProductsAndServicesDomain_1501ff26-b142-49ec-a63c-2fb449a118f3_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ProductsAndServicesDomain_1efb804a-c79d-49f4-8716-1c7ec1af9691" xlink:href="http://xbrl.fasb.org/srt/2019/elts/srt-2019-01-31.xsd#srt_ProductsAndServicesDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_ProductOrServiceAxis_1501ff26-b142-49ec-a63c-2fb449a118f3" xlink:to="loc_srt_ProductsAndServicesDomain_1efb804a-c79d-49f4-8716-1c7ec1af9691" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_cmc_SteelProductsMember_8549af19-c883-4d3d-b9a6-c4bbe36bac03" xlink:href="cmc-20200229.xsd#cmc_SteelProductsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ProductsAndServicesDomain_1efb804a-c79d-49f4-8716-1c7ec1af9691" xlink:to="loc_cmc_SteelProductsMember_8549af19-c883-4d3d-b9a6-c4bbe36bac03" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_cmc_FerrousScrapMember_f013c6fb-17ba-423f-a089-0053a8ae314d" xlink:href="cmc-20200229.xsd#cmc_FerrousScrapMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ProductsAndServicesDomain_1efb804a-c79d-49f4-8716-1c7ec1af9691" xlink:to="loc_cmc_FerrousScrapMember_f013c6fb-17ba-423f-a089-0053a8ae314d" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_cmc_NonferrousScrapMember_429b4397-6a24-4369-b194-12f16c4ba286" xlink:href="cmc-20200229.xsd#cmc_NonferrousScrapMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ProductsAndServicesDomain_1efb804a-c79d-49f4-8716-1c7ec1af9691" xlink:to="loc_cmc_NonferrousScrapMember_429b4397-6a24-4369-b194-12f16c4ba286" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_cmc_ConstructionMaterialsMember_502e70b3-5c47-40d2-a797-b28228daf3c1" xlink:href="cmc-20200229.xsd#cmc_ConstructionMaterialsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ProductsAndServicesDomain_1efb804a-c79d-49f4-8716-1c7ec1af9691" xlink:to="loc_cmc_ConstructionMaterialsMember_502e70b3-5c47-40d2-a797-b28228daf3c1" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_cmc_OtherProductMember_62c87fe0-8c2d-4780-8116-760decda0214" xlink:href="cmc-20200229.xsd#cmc_OtherProductMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ProductsAndServicesDomain_1efb804a-c79d-49f4-8716-1c7ec1af9691" xlink:to="loc_cmc_OtherProductMember_62c87fe0-8c2d-4780-8116-760decda0214" xlink:type="arc" order="4"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.cmc.com/role/INVENTORIESNET" xlink:type="simple" xlink:href="cmc-20200229.xsd#INVENTORIESNET"/>
  <link:definitionLink xlink:role="http://www.cmc.com/role/INVENTORIESNET" xlink:type="extended" id="i2fea5757b6d14259a4d2e9bc1480566f_a766ac9b-d5fd-4081-8376-e22ff3c7e1a2"/>
  <link:roleRef roleURI="http://www.cmc.com/role/INVENTORIESNETNarrativeDetails" xlink:type="simple" xlink:href="cmc-20200229.xsd#INVENTORIESNETNarrativeDetails"/>
  <link:definitionLink xlink:role="http://www.cmc.com/role/INVENTORIESNETNarrativeDetails" xlink:type="extended" id="ic0439b54785d4f139e26dc9f52c0d24f_6dad2502-47e4-43c8-8c7c-df95aa02099b"/>
  <link:roleRef roleURI="http://www.cmc.com/role/GOODWILLANDOTHERINTANGIBLES" xlink:type="simple" xlink:href="cmc-20200229.xsd#GOODWILLANDOTHERINTANGIBLES"/>
  <link:definitionLink xlink:role="http://www.cmc.com/role/GOODWILLANDOTHERINTANGIBLES" xlink:type="extended" id="i6520455eb5b74f65ad029b1c36c9e5d9_2fad17f5-7820-40f2-80d0-7fc311ab4bf3"/>
  <link:roleRef roleURI="http://www.cmc.com/role/GOODWILLANDOTHERINTANGIBLESTables" xlink:type="simple" xlink:href="cmc-20200229.xsd#GOODWILLANDOTHERINTANGIBLESTables"/>
  <link:definitionLink xlink:role="http://www.cmc.com/role/GOODWILLANDOTHERINTANGIBLESTables" xlink:type="extended" id="i59181553c7c8431891d477af2f247e88_268a8709-1743-4675-9a44-12182d450804"/>
  <link:roleRef roleURI="http://www.cmc.com/role/GOODWILLANDOTHERINTANGIBLESNarrativeDetails" xlink:type="simple" xlink:href="cmc-20200229.xsd#GOODWILLANDOTHERINTANGIBLESNarrativeDetails"/>
  <link:definitionLink xlink:role="http://www.cmc.com/role/GOODWILLANDOTHERINTANGIBLESNarrativeDetails" xlink:type="extended" id="ibb68274ccebf4cebaa34686dc7206148_bf5b3e96-291b-4307-a7a3-17336c2af7f7"/>
  <link:roleRef roleURI="http://www.cmc.com/role/GOODWILLANDOTHERINTANGIBLESChangesintheCarryingAmountofGoodwillDetails" xlink:type="simple" xlink:href="cmc-20200229.xsd#GOODWILLANDOTHERINTANGIBLESChangesintheCarryingAmountofGoodwillDetails"/>
  <link:definitionLink xlink:role="http://www.cmc.com/role/GOODWILLANDOTHERINTANGIBLESChangesintheCarryingAmountofGoodwillDetails" xlink:type="extended" id="i231b0d1e3f30451cacc99f2a04a4be55_2e14a4b5-de7f-4215-b331-9df0f9d9f9e2">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_GoodwillLineItems_a1a9c8c6-0eb4-4c38-b4a9-e9f85176d910" xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_GoodwillLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_GoodwillGross_643774a2-2ebb-42d7-8952-23629fbfaa90" xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_GoodwillGross"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_GoodwillLineItems_a1a9c8c6-0eb4-4c38-b4a9-e9f85176d910" xlink:to="loc_us-gaap_GoodwillGross_643774a2-2ebb-42d7-8952-23629fbfaa90" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_GoodwillImpairedAccumulatedImpairmentLoss_58aebe65-61ef-463d-9125-a5ef5265f50a" xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_GoodwillImpairedAccumulatedImpairmentLoss"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_GoodwillLineItems_a1a9c8c6-0eb4-4c38-b4a9-e9f85176d910" xlink:to="loc_us-gaap_GoodwillImpairedAccumulatedImpairmentLoss_58aebe65-61ef-463d-9125-a5ef5265f50a" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_Goodwill_b28de305-ad22-43eb-9ec0-fa76d976f09e" xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_Goodwill"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_GoodwillLineItems_a1a9c8c6-0eb4-4c38-b4a9-e9f85176d910" xlink:to="loc_us-gaap_Goodwill_b28de305-ad22-43eb-9ec0-fa76d976f09e" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfGoodwillTable_78fb0b81-eacf-41fe-936a-36284be9e109" xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_ScheduleOfGoodwillTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_GoodwillLineItems_a1a9c8c6-0eb4-4c38-b4a9-e9f85176d910" xlink:to="loc_us-gaap_ScheduleOfGoodwillTable_78fb0b81-eacf-41fe-936a-36284be9e109" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementBusinessSegmentsAxis_4e4588b7-67df-4b15-9a38-dc4cc55a2a34" xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_StatementBusinessSegmentsAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfGoodwillTable_78fb0b81-eacf-41fe-936a-36284be9e109" xlink:to="loc_us-gaap_StatementBusinessSegmentsAxis_4e4588b7-67df-4b15-9a38-dc4cc55a2a34" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SegmentDomain_4e4588b7-67df-4b15-9a38-dc4cc55a2a34_default" xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_SegmentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_StatementBusinessSegmentsAxis_4e4588b7-67df-4b15-9a38-dc4cc55a2a34" xlink:to="loc_us-gaap_SegmentDomain_4e4588b7-67df-4b15-9a38-dc4cc55a2a34_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SegmentDomain_76dbccd0-f962-43af-a6f0-dbd7b0d46bd9" xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_SegmentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_StatementBusinessSegmentsAxis_4e4588b7-67df-4b15-9a38-dc4cc55a2a34" xlink:to="loc_us-gaap_SegmentDomain_76dbccd0-f962-43af-a6f0-dbd7b0d46bd9" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_cmc_AmericasRecyclingMember_c50a9887-9ad4-4946-9d73-ae2c67e0161d" xlink:href="cmc-20200229.xsd#cmc_AmericasRecyclingMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentDomain_76dbccd0-f962-43af-a6f0-dbd7b0d46bd9" xlink:to="loc_cmc_AmericasRecyclingMember_c50a9887-9ad4-4946-9d73-ae2c67e0161d" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_cmc_AmericasMillsMember_36be7987-6217-4dd4-b071-796da93ced93" xlink:href="cmc-20200229.xsd#cmc_AmericasMillsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentDomain_76dbccd0-f962-43af-a6f0-dbd7b0d46bd9" xlink:to="loc_cmc_AmericasMillsMember_36be7987-6217-4dd4-b071-796da93ced93" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_cmc_AmericasFabricationMember_39bc3ae8-e29a-4431-8c3a-888bed9d2824" xlink:href="cmc-20200229.xsd#cmc_AmericasFabricationMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentDomain_76dbccd0-f962-43af-a6f0-dbd7b0d46bd9" xlink:to="loc_cmc_AmericasFabricationMember_39bc3ae8-e29a-4431-8c3a-888bed9d2824" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_cmc_InternationalMillsMember_eafc30c4-1718-4a4c-8733-e3823682ca73" xlink:href="cmc-20200229.xsd#cmc_InternationalMillsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentDomain_76dbccd0-f962-43af-a6f0-dbd7b0d46bd9" xlink:to="loc_cmc_InternationalMillsMember_eafc30c4-1718-4a4c-8733-e3823682ca73" xlink:type="arc" order="3"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.cmc.com/role/LEASES" xlink:type="simple" xlink:href="cmc-20200229.xsd#LEASES"/>
  <link:definitionLink xlink:role="http://www.cmc.com/role/LEASES" xlink:type="extended" id="ic359371f66064b2fa8a4e762617435ab_c53abce0-9ae6-4fc2-96a3-e9e6f5c4c10c"/>
  <link:roleRef roleURI="http://www.cmc.com/role/LEASESTables" xlink:type="simple" xlink:href="cmc-20200229.xsd#LEASESTables"/>
  <link:definitionLink xlink:role="http://www.cmc.com/role/LEASESTables" xlink:type="extended" id="i772cd3e66eb54390a97c84a1cd3db45a_2e110e33-6f2d-497e-8f16-e3dcf1f32425"/>
  <link:roleRef roleURI="http://www.cmc.com/role/LEASESBalanceSheetComponentsDetails" xlink:type="simple" xlink:href="cmc-20200229.xsd#LEASESBalanceSheetComponentsDetails"/>
  <link:definitionLink xlink:role="http://www.cmc.com/role/LEASESBalanceSheetComponentsDetails" xlink:type="extended" id="i20ed19dfece64b40adeac5c583011bda_acbd8b45-b795-4762-a1b8-6089c9c8a681"/>
  <link:roleRef roleURI="http://www.cmc.com/role/LEASESLeaseCostDetails" xlink:type="simple" xlink:href="cmc-20200229.xsd#LEASESLeaseCostDetails"/>
  <link:definitionLink xlink:role="http://www.cmc.com/role/LEASESLeaseCostDetails" xlink:type="extended" id="idf184b6fa48b453881d28e47fc6ddcbf_f788a054-d3c6-4b3e-bb00-75edae8c3928"/>
  <link:roleRef roleURI="http://www.cmc.com/role/LEASESWeightedAverageLeaseTermsandDiscountRatesDetails" xlink:type="simple" xlink:href="cmc-20200229.xsd#LEASESWeightedAverageLeaseTermsandDiscountRatesDetails"/>
  <link:definitionLink xlink:role="http://www.cmc.com/role/LEASESWeightedAverageLeaseTermsandDiscountRatesDetails" xlink:type="extended" id="iead6e310c62b48508c4ee5cbf0ea6524_7c674e2a-a737-4d7c-8aea-2443a0d6b4b1"/>
  <link:roleRef roleURI="http://www.cmc.com/role/LEASESCashFlowandOtherInformationRelatedtoLeasesDetails" xlink:type="simple" xlink:href="cmc-20200229.xsd#LEASESCashFlowandOtherInformationRelatedtoLeasesDetails"/>
  <link:definitionLink xlink:role="http://www.cmc.com/role/LEASESCashFlowandOtherInformationRelatedtoLeasesDetails" xlink:type="extended" id="i4d844e4a70d24a8aa6353796824d4514_1df3a481-7a28-4e30-bd21-a689850800a9"/>
  <link:roleRef roleURI="http://www.cmc.com/role/LEASESMaturityofLeaseLiabilitiesDetails" xlink:type="simple" xlink:href="cmc-20200229.xsd#LEASESMaturityofLeaseLiabilitiesDetails"/>
  <link:definitionLink xlink:role="http://www.cmc.com/role/LEASESMaturityofLeaseLiabilitiesDetails" xlink:type="extended" id="i0cf949390ef24944b168f56275991314_1f972067-8c1d-4335-89a8-b596a52a0ad5"/>
  <link:roleRef roleURI="http://www.cmc.com/role/LEASESFutureLeaseObligationsPriortoAdoptionofASU201602Details" xlink:type="simple" xlink:href="cmc-20200229.xsd#LEASESFutureLeaseObligationsPriortoAdoptionofASU201602Details"/>
  <link:definitionLink xlink:role="http://www.cmc.com/role/LEASESFutureLeaseObligationsPriortoAdoptionofASU201602Details" xlink:type="extended" id="i60f424d7551f4e90a3ad8b302df07ba8_5379a560-665e-409a-ab74-0f3d0a448d68"/>
  <link:roleRef roleURI="http://www.cmc.com/role/CREDITARRANGEMENTS" xlink:type="simple" xlink:href="cmc-20200229.xsd#CREDITARRANGEMENTS"/>
  <link:definitionLink xlink:role="http://www.cmc.com/role/CREDITARRANGEMENTS" xlink:type="extended" id="ia15aaf62dd244de98e114eab1b2b02aa_8350c10b-c16b-4a53-a607-4b00887d6607"/>
  <link:roleRef roleURI="http://www.cmc.com/role/CREDITARRANGEMENTSTables" xlink:type="simple" xlink:href="cmc-20200229.xsd#CREDITARRANGEMENTSTables"/>
  <link:definitionLink xlink:role="http://www.cmc.com/role/CREDITARRANGEMENTSTables" xlink:type="extended" id="i136cebc823794c6caf1e4c3650276e57_ec1c78c1-d19b-41a8-8149-0fc68b8582d6"/>
  <link:roleRef roleURI="http://www.cmc.com/role/CREDITARRANGEMENTSLongtermDebtIncludingtheDeferredGainfromtheTerminationoftheInterestRateSwapsDetails" xlink:type="simple" xlink:href="cmc-20200229.xsd#CREDITARRANGEMENTSLongtermDebtIncludingtheDeferredGainfromtheTerminationoftheInterestRateSwapsDetails"/>
  <link:definitionLink xlink:role="http://www.cmc.com/role/CREDITARRANGEMENTSLongtermDebtIncludingtheDeferredGainfromtheTerminationoftheInterestRateSwapsDetails" xlink:type="extended" id="i1e09f511de0f476c96f53cd0c91825c9_ae0d22fc-7303-4931-8162-e026f9d63f16">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentLineItems_5cbe5477-8e1e-44c3-9fb1-2aa5839d2d08" xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_DebtInstrumentLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongtermDebtWeightedAverageInterestRate_a5716df4-9cae-427e-8378-478c9b8851dd" xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_LongtermDebtWeightedAverageInterestRate"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_5cbe5477-8e1e-44c3-9fb1-2aa5839d2d08" xlink:to="loc_us-gaap_LongtermDebtWeightedAverageInterestRate_a5716df4-9cae-427e-8378-478c9b8851dd" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShortTermDebtWeightedAverageInterestRate_3751fdb7-29e6-4ef2-940b-016788411423" xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_ShortTermDebtWeightedAverageInterestRate"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_5cbe5477-8e1e-44c3-9fb1-2aa5839d2d08" xlink:to="loc_us-gaap_ShortTermDebtWeightedAverageInterestRate_3751fdb7-29e6-4ef2-940b-016788411423" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtAndCapitalLeaseObligations_8dd79151-f234-4ae8-96a4-7fa35cfc7a35" xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_DebtAndCapitalLeaseObligations"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_5cbe5477-8e1e-44c3-9fb1-2aa5839d2d08" xlink:to="loc_us-gaap_DebtAndCapitalLeaseObligations_8dd79151-f234-4ae8-96a4-7fa35cfc7a35" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DeferredFinanceCostsNet_94bd4d28-f7fc-4286-89dc-1844206d5a35" xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_DeferredFinanceCostsNet"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_5cbe5477-8e1e-44c3-9fb1-2aa5839d2d08" xlink:to="loc_us-gaap_DeferredFinanceCostsNet_94bd4d28-f7fc-4286-89dc-1844206d5a35" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_cmc_LongtermDebtandCapitalLeaseObligationsNet_6299c6a8-771c-44fb-856e-aee875c93dd3" xlink:href="cmc-20200229.xsd#cmc_LongtermDebtandCapitalLeaseObligationsNet"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_5cbe5477-8e1e-44c3-9fb1-2aa5839d2d08" xlink:to="loc_cmc_LongtermDebtandCapitalLeaseObligationsNet_6299c6a8-771c-44fb-856e-aee875c93dd3" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongTermDebtAndCapitalLeaseObligationsCurrent_8c8a3690-ebca-4ae2-8cfd-3744d3c0c05e" xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_LongTermDebtAndCapitalLeaseObligationsCurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_5cbe5477-8e1e-44c3-9fb1-2aa5839d2d08" xlink:to="loc_us-gaap_LongTermDebtAndCapitalLeaseObligationsCurrent_8c8a3690-ebca-4ae2-8cfd-3744d3c0c05e" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShortTermBorrowings_fe36be98-eb98-446e-a1e7-5a6bd958d7ec" xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_ShortTermBorrowings"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_5cbe5477-8e1e-44c3-9fb1-2aa5839d2d08" xlink:to="loc_us-gaap_ShortTermBorrowings_fe36be98-eb98-446e-a1e7-5a6bd958d7ec" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_cmc_CurrentMaturitiesandShorttermBorrowings_be7d6ca4-c731-4d12-9398-9d7f27d53378" xlink:href="cmc-20200229.xsd#cmc_CurrentMaturitiesandShorttermBorrowings"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_5cbe5477-8e1e-44c3-9fb1-2aa5839d2d08" xlink:to="loc_cmc_CurrentMaturitiesandShorttermBorrowings_be7d6ca4-c731-4d12-9398-9d7f27d53378" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongTermDebtAndCapitalLeaseObligations_0fbc8c1b-290f-4cf0-af48-9ef58117fbf3" xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_LongTermDebtAndCapitalLeaseObligations"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_5cbe5477-8e1e-44c3-9fb1-2aa5839d2d08" xlink:to="loc_us-gaap_LongTermDebtAndCapitalLeaseObligations_0fbc8c1b-290f-4cf0-af48-9ef58117fbf3" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_cmc_DepreciationAmortizationAndAssetImpairmentCharges_fab49db9-be79-4afa-896e-0235eb85400e" xlink:href="cmc-20200229.xsd#cmc_DepreciationAmortizationAndAssetImpairmentCharges"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_5cbe5477-8e1e-44c3-9fb1-2aa5839d2d08" xlink:to="loc_cmc_DepreciationAmortizationAndAssetImpairmentCharges_fab49db9-be79-4afa-896e-0235eb85400e" xlink:type="arc" order="9"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentTable_792d624b-f9be-438e-9124-991d6ed334e4" xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_DebtInstrumentTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_DebtInstrumentLineItems_5cbe5477-8e1e-44c3-9fb1-2aa5839d2d08" xlink:to="loc_us-gaap_DebtInstrumentTable_792d624b-f9be-438e-9124-991d6ed334e4" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongtermDebtTypeAxis_4663c32e-c2f1-4c32-8fd5-368dbaf515f5" xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_LongtermDebtTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DebtInstrumentTable_792d624b-f9be-438e-9124-991d6ed334e4" xlink:to="loc_us-gaap_LongtermDebtTypeAxis_4663c32e-c2f1-4c32-8fd5-368dbaf515f5" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongtermDebtTypeDomain_4663c32e-c2f1-4c32-8fd5-368dbaf515f5_default" xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_LongtermDebtTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_LongtermDebtTypeAxis_4663c32e-c2f1-4c32-8fd5-368dbaf515f5" xlink:to="loc_us-gaap_LongtermDebtTypeDomain_4663c32e-c2f1-4c32-8fd5-368dbaf515f5_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongtermDebtTypeDomain_6f8e6212-170d-4e50-a598-b6c804078586" xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_LongtermDebtTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_LongtermDebtTypeAxis_4663c32e-c2f1-4c32-8fd5-368dbaf515f5" xlink:to="loc_us-gaap_LongtermDebtTypeDomain_6f8e6212-170d-4e50-a598-b6c804078586" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_cmc_A300MillionNotesat5.375dueJuly2027Member_8d3de119-3726-4332-be8b-36344b7e615a" xlink:href="cmc-20200229.xsd#cmc_A300MillionNotesat5.375dueJuly2027Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LongtermDebtTypeDomain_6f8e6212-170d-4e50-a598-b6c804078586" xlink:to="loc_cmc_A300MillionNotesat5.375dueJuly2027Member_8d3de119-3726-4332-be8b-36344b7e615a" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_cmc_A350millionnotesat5.75dueApril2026Member_9af59637-88c2-46dd-9d77-eb637a0db918" xlink:href="cmc-20200229.xsd#cmc_A350millionnotesat5.75dueApril2026Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LongtermDebtTypeDomain_6f8e6212-170d-4e50-a598-b6c804078586" xlink:to="loc_cmc_A350millionnotesat5.75dueApril2026Member_9af59637-88c2-46dd-9d77-eb637a0db918" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_cmc_A330MillionNotesAt4875DueMay2023Member_081c14ca-a5bd-4eb6-bd31-878b305d5afd" xlink:href="cmc-20200229.xsd#cmc_A330MillionNotesAt4875DueMay2023Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LongtermDebtTypeDomain_6f8e6212-170d-4e50-a598-b6c804078586" xlink:to="loc_cmc_A330MillionNotesAt4875DueMay2023Member_081c14ca-a5bd-4eb6-bd31-878b305d5afd" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_MediumTermNotesMember_74e1d12e-e6b1-4c80-95bf-998b795864ce" xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_MediumTermNotesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LongtermDebtTypeDomain_6f8e6212-170d-4e50-a598-b6c804078586" xlink:to="loc_us-gaap_MediumTermNotesMember_74e1d12e-e6b1-4c80-95bf-998b795864ce" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_cmc_PolandCreditFacilitiesMember_6cda2845-461d-4c19-af38-d2f9472741f0" xlink:href="cmc-20200229.xsd#cmc_PolandCreditFacilitiesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LongtermDebtTypeDomain_6f8e6212-170d-4e50-a598-b6c804078586" xlink:to="loc_cmc_PolandCreditFacilitiesMember_6cda2845-461d-4c19-af38-d2f9472741f0" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShortTermDebtMember_3df69aeb-4024-404f-9e94-60944066c2bb" xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_ShortTermDebtMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LongtermDebtTypeDomain_6f8e6212-170d-4e50-a598-b6c804078586" xlink:to="loc_us-gaap_ShortTermDebtMember_3df69aeb-4024-404f-9e94-60944066c2bb" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_cmc_OtherDebtMember_650cf931-2071-4485-b270-46d3043f89aa" xlink:href="cmc-20200229.xsd#cmc_OtherDebtMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LongtermDebtTypeDomain_6f8e6212-170d-4e50-a598-b6c804078586" xlink:to="loc_cmc_OtherDebtMember_650cf931-2071-4485-b270-46d3043f89aa" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_cmc_FinanceLeasesMember_66fc44ce-b959-4da2-a813-f8684d6256b5" xlink:href="cmc-20200229.xsd#cmc_FinanceLeasesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LongtermDebtTypeDomain_6f8e6212-170d-4e50-a598-b6c804078586" xlink:to="loc_cmc_FinanceLeasesMember_66fc44ce-b959-4da2-a813-f8684d6256b5" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CreditFacilityAxis_408a06a1-3f00-4f10-956c-f1752cbfbef1" xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_CreditFacilityAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DebtInstrumentTable_792d624b-f9be-438e-9124-991d6ed334e4" xlink:to="loc_us-gaap_CreditFacilityAxis_408a06a1-3f00-4f10-956c-f1752cbfbef1" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CreditFacilityDomain_408a06a1-3f00-4f10-956c-f1752cbfbef1_default" xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_CreditFacilityDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_CreditFacilityAxis_408a06a1-3f00-4f10-956c-f1752cbfbef1" xlink:to="loc_us-gaap_CreditFacilityDomain_408a06a1-3f00-4f10-956c-f1752cbfbef1_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CreditFacilityDomain_5716f7fc-7df5-4d19-9cb2-ea91003ab114" xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_CreditFacilityDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_CreditFacilityAxis_408a06a1-3f00-4f10-956c-f1752cbfbef1" xlink:to="loc_us-gaap_CreditFacilityDomain_5716f7fc-7df5-4d19-9cb2-ea91003ab114" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RevolvingCreditFacilityMember_dd9f5b50-c749-49ab-aa7d-8d80e41d80ae" xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_RevolvingCreditFacilityMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_CreditFacilityDomain_5716f7fc-7df5-4d19-9cb2-ea91003ab114" xlink:to="loc_us-gaap_RevolvingCreditFacilityMember_dd9f5b50-c749-49ab-aa7d-8d80e41d80ae" xlink:type="arc" order="0"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.cmc.com/role/CREDITARRANGEMENTSNarrativeDetails" xlink:type="simple" xlink:href="cmc-20200229.xsd#CREDITARRANGEMENTSNarrativeDetails"/>
  <link:definitionLink xlink:role="http://www.cmc.com/role/CREDITARRANGEMENTSNarrativeDetails" xlink:type="extended" id="if9a50782e09d44f5be910d4ce72e0503_490a5609-17bc-4222-a1c3-fec604919b3f">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentLineItems_2dfe0155-ad44-4678-ad82-36ca20158867" xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_DebtInstrumentLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LineOfCreditFacilityCurrentBorrowingCapacity_88f510d8-0d2c-4648-a4c2-41ecc369eb38" xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_LineOfCreditFacilityCurrentBorrowingCapacity"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_2dfe0155-ad44-4678-ad82-36ca20158867" xlink:to="loc_us-gaap_LineOfCreditFacilityCurrentBorrowingCapacity_88f510d8-0d2c-4648-a4c2-41ecc369eb38" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LineOfCreditFacilityFairValueOfAmountOutstanding_df32bbec-00db-44e7-bfdf-190d608b1cdf" xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_LineOfCreditFacilityFairValueOfAmountOutstanding"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_2dfe0155-ad44-4678-ad82-36ca20158867" xlink:to="loc_us-gaap_LineOfCreditFacilityFairValueOfAmountOutstanding_df32bbec-00db-44e7-bfdf-190d608b1cdf" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LettersOfCreditOutstandingAmount_20e114dd-88a1-4103-8132-15da16f30461" xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_LettersOfCreditOutstandingAmount"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_2dfe0155-ad44-4678-ad82-36ca20158867" xlink:to="loc_us-gaap_LettersOfCreditOutstandingAmount_20e114dd-88a1-4103-8132-15da16f30461" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_cmc_TransferofAccountsReceivableProgramFaceAmount_67921de3-c423-44d5-b3bf-002330b26a7c" xlink:href="cmc-20200229.xsd#cmc_TransferofAccountsReceivableProgramFaceAmount"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_2dfe0155-ad44-4678-ad82-36ca20158867" xlink:to="loc_cmc_TransferofAccountsReceivableProgramFaceAmount_67921de3-c423-44d5-b3bf-002330b26a7c" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_cmc_TransfersofAccountsReceivableOutstanding_16442951-e643-430f-b6ec-7245fe82b0ab" xlink:href="cmc-20200229.xsd#cmc_TransfersofAccountsReceivableOutstanding"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_2dfe0155-ad44-4678-ad82-36ca20158867" xlink:to="loc_cmc_TransfersofAccountsReceivableOutstanding_16442951-e643-430f-b6ec-7245fe82b0ab" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentTable_a95e927a-da63-486c-88f9-951c8ebfd331" xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_DebtInstrumentTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_DebtInstrumentLineItems_2dfe0155-ad44-4678-ad82-36ca20158867" xlink:to="loc_us-gaap_DebtInstrumentTable_a95e927a-da63-486c-88f9-951c8ebfd331" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentAxis_88ecc47f-37c6-470d-8682-4f30a30737f6" xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_DebtInstrumentAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DebtInstrumentTable_a95e927a-da63-486c-88f9-951c8ebfd331" xlink:to="loc_us-gaap_DebtInstrumentAxis_88ecc47f-37c6-470d-8682-4f30a30737f6" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentNameDomain_88ecc47f-37c6-470d-8682-4f30a30737f6_default" xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_DebtInstrumentNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_DebtInstrumentAxis_88ecc47f-37c6-470d-8682-4f30a30737f6" xlink:to="loc_us-gaap_DebtInstrumentNameDomain_88ecc47f-37c6-470d-8682-4f30a30737f6_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentNameDomain_edb8fac5-bee2-44d8-ac21-42d2d2724a75" xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_DebtInstrumentNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_DebtInstrumentAxis_88ecc47f-37c6-470d-8682-4f30a30737f6" xlink:to="loc_us-gaap_DebtInstrumentNameDomain_edb8fac5-bee2-44d8-ac21-42d2d2724a75" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_cmc_U.S.ProgramMember_f2f0437a-ac4d-4ee3-865d-a0d51ab2fa01" xlink:href="cmc-20200229.xsd#cmc_U.S.ProgramMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_edb8fac5-bee2-44d8-ac21-42d2d2724a75" xlink:to="loc_cmc_U.S.ProgramMember_f2f0437a-ac4d-4ee3-865d-a0d51ab2fa01" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_cmc_PolandProgramMember_1e2a16bb-d147-4439-b994-f836f0ae9c0f" xlink:href="cmc-20200229.xsd#cmc_PolandProgramMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_edb8fac5-bee2-44d8-ac21-42d2d2724a75" xlink:to="loc_cmc_PolandProgramMember_1e2a16bb-d147-4439-b994-f836f0ae9c0f" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CreditFacilityAxis_d762f525-201d-4f07-a5e7-db1f4f01b9e0" xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_CreditFacilityAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DebtInstrumentTable_a95e927a-da63-486c-88f9-951c8ebfd331" xlink:to="loc_us-gaap_CreditFacilityAxis_d762f525-201d-4f07-a5e7-db1f4f01b9e0" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CreditFacilityDomain_d762f525-201d-4f07-a5e7-db1f4f01b9e0_default" xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_CreditFacilityDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_CreditFacilityAxis_d762f525-201d-4f07-a5e7-db1f4f01b9e0" xlink:to="loc_us-gaap_CreditFacilityDomain_d762f525-201d-4f07-a5e7-db1f4f01b9e0_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CreditFacilityDomain_a03f377e-14b7-45ee-b824-102762c0bda3" xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_CreditFacilityDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_CreditFacilityAxis_d762f525-201d-4f07-a5e7-db1f4f01b9e0" xlink:to="loc_us-gaap_CreditFacilityDomain_a03f377e-14b7-45ee-b824-102762c0bda3" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RevolvingCreditFacilityMember_a137b26d-9e6c-436f-b299-a7d94a4ed9fb" xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_RevolvingCreditFacilityMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_CreditFacilityDomain_a03f377e-14b7-45ee-b824-102762c0bda3" xlink:to="loc_us-gaap_RevolvingCreditFacilityMember_a137b26d-9e6c-436f-b299-a7d94a4ed9fb" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LetterOfCreditMember_5cc0df16-0843-47db-8f61-456c1da09dd5" xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_LetterOfCreditMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RevolvingCreditFacilityMember_a137b26d-9e6c-436f-b299-a7d94a4ed9fb" xlink:to="loc_us-gaap_LetterOfCreditMember_5cc0df16-0843-47db-8f61-456c1da09dd5" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_LegalEntityAxis_41795440-0f99-4de1-a061-7fcb8b2b5849" xlink:href="https://xbrl.sec.gov/dei/2019/dei-2019-01-31.xsd#dei_LegalEntityAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DebtInstrumentTable_a95e927a-da63-486c-88f9-951c8ebfd331" xlink:to="loc_dei_LegalEntityAxis_41795440-0f99-4de1-a061-7fcb8b2b5849" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityDomain_41795440-0f99-4de1-a061-7fcb8b2b5849_default" xlink:href="https://xbrl.sec.gov/dei/2019/dei-2019-01-31.xsd#dei_EntityDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_dei_LegalEntityAxis_41795440-0f99-4de1-a061-7fcb8b2b5849" xlink:to="loc_dei_EntityDomain_41795440-0f99-4de1-a061-7fcb8b2b5849_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityDomain_f63622a0-b6ee-4374-a8f1-20842f2a3da2" xlink:href="https://xbrl.sec.gov/dei/2019/dei-2019-01-31.xsd#dei_EntityDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_dei_LegalEntityAxis_41795440-0f99-4de1-a061-7fcb8b2b5849" xlink:to="loc_dei_EntityDomain_f63622a0-b6ee-4374-a8f1-20842f2a3da2" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_cmc_CmcpMember_d59d12c2-849e-4c33-a3e2-9fa1ce679a09" xlink:href="cmc-20200229.xsd#cmc_CmcpMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityDomain_f63622a0-b6ee-4374-a8f1-20842f2a3da2" xlink:to="loc_cmc_CmcpMember_d59d12c2-849e-4c33-a3e2-9fa1ce679a09" xlink:type="arc" order="0"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.cmc.com/role/DERIVATIVES" xlink:type="simple" xlink:href="cmc-20200229.xsd#DERIVATIVES"/>
  <link:definitionLink xlink:role="http://www.cmc.com/role/DERIVATIVES" xlink:type="extended" id="ie5e66fe5d17e42eb80bea785e3ba6d7e_184cefac-a216-4b81-8ce4-59b6afbb0455"/>
  <link:roleRef roleURI="http://www.cmc.com/role/DERIVATIVESTables" xlink:type="simple" xlink:href="cmc-20200229.xsd#DERIVATIVESTables"/>
  <link:definitionLink xlink:role="http://www.cmc.com/role/DERIVATIVESTables" xlink:type="extended" id="i55001473e1d141a59b95896c97a87691_50768a27-45d1-4bfd-a7ac-4d5984b6935c"/>
  <link:roleRef roleURI="http://www.cmc.com/role/DERIVATIVESNarrativeDetails" xlink:type="simple" xlink:href="cmc-20200229.xsd#DERIVATIVESNarrativeDetails"/>
  <link:definitionLink xlink:role="http://www.cmc.com/role/DERIVATIVESNarrativeDetails" xlink:type="extended" id="idb72dbcfc70b41d091c195610097030f_a6b3cafe-5034-41f9-b165-c96ec2c02931">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeLineItems_016dd509-4164-4103-b636-449c33c8cfcd" xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_DerivativeLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeNotionalAmount_c665210e-fd33-4949-90c2-df9206a222ce" xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_DerivativeNotionalAmount"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DerivativeLineItems_016dd509-4164-4103-b636-449c33c8cfcd" xlink:to="loc_us-gaap_DerivativeNotionalAmount_c665210e-fd33-4949-90c2-df9206a222ce" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeTable_a0991274-37db-4e4a-8b7e-ebe4bc1327d6" xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_DerivativeTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_DerivativeLineItems_016dd509-4164-4103-b636-449c33c8cfcd" xlink:to="loc_us-gaap_DerivativeTable_a0991274-37db-4e4a-8b7e-ebe4bc1327d6" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeInstrumentRiskAxis_256f040a-03b5-4ccd-920f-8469f4ef7999" xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_DerivativeInstrumentRiskAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DerivativeTable_a0991274-37db-4e4a-8b7e-ebe4bc1327d6" xlink:to="loc_us-gaap_DerivativeInstrumentRiskAxis_256f040a-03b5-4ccd-920f-8469f4ef7999" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeContractTypeDomain_256f040a-03b5-4ccd-920f-8469f4ef7999_default" xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_DerivativeContractTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_DerivativeInstrumentRiskAxis_256f040a-03b5-4ccd-920f-8469f4ef7999" xlink:to="loc_us-gaap_DerivativeContractTypeDomain_256f040a-03b5-4ccd-920f-8469f4ef7999_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeContractTypeDomain_5bb1088d-ecd3-4888-aa23-d9830c167044" xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_DerivativeContractTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_DerivativeInstrumentRiskAxis_256f040a-03b5-4ccd-920f-8469f4ef7999" xlink:to="loc_us-gaap_DerivativeContractTypeDomain_5bb1088d-ecd3-4888-aa23-d9830c167044" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ForeignExchangeContractMember_add14401-6136-4928-b6f4-891a9b5a5564" xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_ForeignExchangeContractMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DerivativeContractTypeDomain_5bb1088d-ecd3-4888-aa23-d9830c167044" xlink:to="loc_us-gaap_ForeignExchangeContractMember_add14401-6136-4928-b6f4-891a9b5a5564" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommodityContractMember_79c0a0ea-44ba-40de-bcb2-8ff5ce6ce0ef" xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_CommodityContractMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DerivativeContractTypeDomain_5bb1088d-ecd3-4888-aa23-d9830c167044" xlink:to="loc_us-gaap_CommodityContractMember_79c0a0ea-44ba-40de-bcb2-8ff5ce6ce0ef" xlink:type="arc" order="1"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.cmc.com/role/DERIVATIVESCommodityContractCommitmentsDetails" xlink:type="simple" xlink:href="cmc-20200229.xsd#DERIVATIVESCommodityContractCommitmentsDetails"/>
  <link:definitionLink xlink:role="http://www.cmc.com/role/DERIVATIVESCommodityContractCommitmentsDetails" xlink:type="extended" id="ia383e7d10f614dd4b19cc1cddc5858f6_babe4c91-3773-4dd9-9252-b7afc2499343">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeLineItems_0f5a398b-0fce-4ba7-88c7-17ca4d2db4ab" xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_DerivativeLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeNonmonetaryNotionalAmountMass_e71b794c-c87d-46ba-83b7-1d8b03dda9ae" xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_DerivativeNonmonetaryNotionalAmountMass"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DerivativeLineItems_0f5a398b-0fce-4ba7-88c7-17ca4d2db4ab" xlink:to="loc_us-gaap_DerivativeNonmonetaryNotionalAmountMass_e71b794c-c87d-46ba-83b7-1d8b03dda9ae" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeNonmonetaryNotionalAmountEnergyMeasure_1cbb5d3b-bb38-4f1a-a91b-a4229eac081d" xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_DerivativeNonmonetaryNotionalAmountEnergyMeasure"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DerivativeLineItems_0f5a398b-0fce-4ba7-88c7-17ca4d2db4ab" xlink:to="loc_us-gaap_DerivativeNonmonetaryNotionalAmountEnergyMeasure_1cbb5d3b-bb38-4f1a-a91b-a4229eac081d" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeTable_ebd3f7b0-f7e4-4cf8-93b9-235e7fd36346" xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_DerivativeTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_DerivativeLineItems_0f5a398b-0fce-4ba7-88c7-17ca4d2db4ab" xlink:to="loc_us-gaap_DerivativeTable_ebd3f7b0-f7e4-4cf8-93b9-235e7fd36346" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeInstrumentRiskAxis_0aaddace-a381-43ec-b95c-b76655d85aef" xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_DerivativeInstrumentRiskAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DerivativeTable_ebd3f7b0-f7e4-4cf8-93b9-235e7fd36346" xlink:to="loc_us-gaap_DerivativeInstrumentRiskAxis_0aaddace-a381-43ec-b95c-b76655d85aef" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeContractTypeDomain_0aaddace-a381-43ec-b95c-b76655d85aef_default" xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_DerivativeContractTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_DerivativeInstrumentRiskAxis_0aaddace-a381-43ec-b95c-b76655d85aef" xlink:to="loc_us-gaap_DerivativeContractTypeDomain_0aaddace-a381-43ec-b95c-b76655d85aef_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeContractTypeDomain_181984b7-218e-4862-82a2-b6b5233b1141" xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_DerivativeContractTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_DerivativeInstrumentRiskAxis_0aaddace-a381-43ec-b95c-b76655d85aef" xlink:to="loc_us-gaap_DerivativeContractTypeDomain_181984b7-218e-4862-82a2-b6b5233b1141" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_cmc_AluminumMember_15f55b78-01c5-4399-87ab-e7bbb5c2ff7f" xlink:href="cmc-20200229.xsd#cmc_AluminumMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DerivativeContractTypeDomain_181984b7-218e-4862-82a2-b6b5233b1141" xlink:to="loc_cmc_AluminumMember_15f55b78-01c5-4399-87ab-e7bbb5c2ff7f" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_cmc_CopperMember_a9138ccf-8ca0-44ea-8f8d-b71c7edab2c7" xlink:href="cmc-20200229.xsd#cmc_CopperMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DerivativeContractTypeDomain_181984b7-218e-4862-82a2-b6b5233b1141" xlink:to="loc_cmc_CopperMember_a9138ccf-8ca0-44ea-8f8d-b71c7edab2c7" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ElectricityMember_3e397781-a999-4240-bc57-b7313f8cc69d" xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_ElectricityMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DerivativeContractTypeDomain_181984b7-218e-4862-82a2-b6b5233b1141" xlink:to="loc_us-gaap_ElectricityMember_3e397781-a999-4240-bc57-b7313f8cc69d" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PositionAxis_6345d1ad-d7cb-47a1-9402-7b098395560c" xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_PositionAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DerivativeTable_ebd3f7b0-f7e4-4cf8-93b9-235e7fd36346" xlink:to="loc_us-gaap_PositionAxis_6345d1ad-d7cb-47a1-9402-7b098395560c" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PositionDomain_6345d1ad-d7cb-47a1-9402-7b098395560c_default" xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_PositionDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_PositionAxis_6345d1ad-d7cb-47a1-9402-7b098395560c" xlink:to="loc_us-gaap_PositionDomain_6345d1ad-d7cb-47a1-9402-7b098395560c_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PositionDomain_0dffcf5b-8179-48e8-b022-189311dd4f5d" xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_PositionDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_PositionAxis_6345d1ad-d7cb-47a1-9402-7b098395560c" xlink:to="loc_us-gaap_PositionDomain_0dffcf5b-8179-48e8-b022-189311dd4f5d" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongMember_c4b8654e-769f-4953-afcd-081b573cf6eb" xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_LongMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PositionDomain_0dffcf5b-8179-48e8-b022-189311dd4f5d" xlink:to="loc_us-gaap_LongMember_c4b8654e-769f-4953-afcd-081b573cf6eb" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShortMember_651d631d-116d-4481-9172-0e7093c0df5d" xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_ShortMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PositionDomain_0dffcf5b-8179-48e8-b022-189311dd4f5d" xlink:to="loc_us-gaap_ShortMember_651d631d-116d-4481-9172-0e7093c0df5d" xlink:type="arc" order="1"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.cmc.com/role/DERIVATIVESDerivativesNotDesignatedasHedgingInstrumentsDetails" xlink:type="simple" xlink:href="cmc-20200229.xsd#DERIVATIVESDerivativesNotDesignatedasHedgingInstrumentsDetails"/>
  <link:definitionLink xlink:role="http://www.cmc.com/role/DERIVATIVESDerivativesNotDesignatedasHedgingInstrumentsDetails" xlink:type="extended" id="ida557d645659412388a551259197ebf0_03e35bc9-19e6-4bdf-8c5d-1259b5ce8caa">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeInstrumentsGainLossLineItems_01546807-b6ff-46d4-9b2e-5ab38f0fc456" xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_DerivativeInstrumentsGainLossLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeInstrumentsNotDesignatedAsHedgingInstrumentsGainLossNet_48ac0136-e30b-477a-82da-0e7d7d1add3f" xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_DerivativeInstrumentsNotDesignatedAsHedgingInstrumentsGainLossNet"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DerivativeInstrumentsGainLossLineItems_01546807-b6ff-46d4-9b2e-5ab38f0fc456" xlink:to="loc_us-gaap_DerivativeInstrumentsNotDesignatedAsHedgingInstrumentsGainLossNet_48ac0136-e30b-477a-82da-0e7d7d1add3f" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeInstrumentsGainLossByHedgingRelationshipByIncomeStatementLocationByDerivativeInstrumentRiskTable_3f8646c6-3348-49d0-9df8-65b8f0a88e53" xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_DerivativeInstrumentsGainLossByHedgingRelationshipByIncomeStatementLocationByDerivativeInstrumentRiskTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_DerivativeInstrumentsGainLossLineItems_01546807-b6ff-46d4-9b2e-5ab38f0fc456" xlink:to="loc_us-gaap_DerivativeInstrumentsGainLossByHedgingRelationshipByIncomeStatementLocationByDerivativeInstrumentRiskTable_3f8646c6-3348-49d0-9df8-65b8f0a88e53" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeInstrumentRiskAxis_3b402914-72fe-4f74-99aa-518c383e9ed8" xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_DerivativeInstrumentRiskAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DerivativeInstrumentsGainLossByHedgingRelationshipByIncomeStatementLocationByDerivativeInstrumentRiskTable_3f8646c6-3348-49d0-9df8-65b8f0a88e53" xlink:to="loc_us-gaap_DerivativeInstrumentRiskAxis_3b402914-72fe-4f74-99aa-518c383e9ed8" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeContractTypeDomain_3b402914-72fe-4f74-99aa-518c383e9ed8_default" xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_DerivativeContractTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_DerivativeInstrumentRiskAxis_3b402914-72fe-4f74-99aa-518c383e9ed8" xlink:to="loc_us-gaap_DerivativeContractTypeDomain_3b402914-72fe-4f74-99aa-518c383e9ed8_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeContractTypeDomain_bf880524-0126-48d2-924a-7e8d91936052" xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_DerivativeContractTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_DerivativeInstrumentRiskAxis_3b402914-72fe-4f74-99aa-518c383e9ed8" xlink:to="loc_us-gaap_DerivativeContractTypeDomain_bf880524-0126-48d2-924a-7e8d91936052" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommodityContractMember_63115ece-5d81-442a-b14e-f0150735eea2" xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_CommodityContractMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DerivativeContractTypeDomain_bf880524-0126-48d2-924a-7e8d91936052" xlink:to="loc_us-gaap_CommodityContractMember_63115ece-5d81-442a-b14e-f0150735eea2" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ForeignExchangeContractMember_ac68bc7e-15aa-46fa-b362-0fee94ea53d9" xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_ForeignExchangeContractMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DerivativeContractTypeDomain_bf880524-0126-48d2-924a-7e8d91936052" xlink:to="loc_us-gaap_ForeignExchangeContractMember_ac68bc7e-15aa-46fa-b362-0fee94ea53d9" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeStatementLocationAxis_47041be4-91d5-4c5b-b9b6-78d840a978b4" xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_IncomeStatementLocationAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DerivativeInstrumentsGainLossByHedgingRelationshipByIncomeStatementLocationByDerivativeInstrumentRiskTable_3f8646c6-3348-49d0-9df8-65b8f0a88e53" xlink:to="loc_us-gaap_IncomeStatementLocationAxis_47041be4-91d5-4c5b-b9b6-78d840a978b4" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeStatementLocationDomain_47041be4-91d5-4c5b-b9b6-78d840a978b4_default" xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_IncomeStatementLocationDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_IncomeStatementLocationAxis_47041be4-91d5-4c5b-b9b6-78d840a978b4" xlink:to="loc_us-gaap_IncomeStatementLocationDomain_47041be4-91d5-4c5b-b9b6-78d840a978b4_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeStatementLocationDomain_24b3f67d-424e-4b31-a51a-992e47665888" xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_IncomeStatementLocationDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_IncomeStatementLocationAxis_47041be4-91d5-4c5b-b9b6-78d840a978b4" xlink:to="loc_us-gaap_IncomeStatementLocationDomain_24b3f67d-424e-4b31-a51a-992e47665888" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CostOfSalesMember_501a0fbe-79da-4a79-ae01-19fda443a7dd" xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_CostOfSalesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncomeStatementLocationDomain_24b3f67d-424e-4b31-a51a-992e47665888" xlink:to="loc_us-gaap_CostOfSalesMember_501a0fbe-79da-4a79-ae01-19fda443a7dd" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OperatingExpenseMember_c669b156-8e5b-41b0-b5a8-1d4d10eed906" xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_OperatingExpenseMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncomeStatementLocationDomain_24b3f67d-424e-4b31-a51a-992e47665888" xlink:to="loc_us-gaap_OperatingExpenseMember_c669b156-8e5b-41b0-b5a8-1d4d10eed906" xlink:type="arc" order="1"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.cmc.com/role/FAIRVALUE" xlink:type="simple" xlink:href="cmc-20200229.xsd#FAIRVALUE"/>
  <link:definitionLink xlink:role="http://www.cmc.com/role/FAIRVALUE" xlink:type="extended" id="i67011efc0c3447e189a0114743c7be66_b5606c89-0d78-4e00-a3ff-6f0950b2cdad"/>
  <link:roleRef roleURI="http://www.cmc.com/role/FAIRVALUETables" xlink:type="simple" xlink:href="cmc-20200229.xsd#FAIRVALUETables"/>
  <link:definitionLink xlink:role="http://www.cmc.com/role/FAIRVALUETables" xlink:type="extended" id="icf991133b8b3456387c1792520d988ec_53d8a493-1a1b-4847-b36c-71dbba505986"/>
  <link:roleRef roleURI="http://www.cmc.com/role/FAIRVALUENarrativeDetails" xlink:type="simple" xlink:href="cmc-20200229.xsd#FAIRVALUENarrativeDetails"/>
  <link:definitionLink xlink:role="http://www.cmc.com/role/FAIRVALUENarrativeDetails" xlink:type="extended" id="ic24dbccfcaee4985934005f14be1203b_8ce45f73-f8ba-4131-8b87-1070f5406182"/>
  <link:roleRef roleURI="http://www.cmc.com/role/FAIRVALUEFinancialAssetsandFinancialLiabilitiesMeasuredatFairValueonRecurringBasisDetails" xlink:type="simple" xlink:href="cmc-20200229.xsd#FAIRVALUEFinancialAssetsandFinancialLiabilitiesMeasuredatFairValueonRecurringBasisDetails"/>
  <link:definitionLink xlink:role="http://www.cmc.com/role/FAIRVALUEFinancialAssetsandFinancialLiabilitiesMeasuredatFairValueonRecurringBasisDetails" xlink:type="extended" id="ibdf992c0e32d4e1ab4ffc5fc20b76302_2176d990-9260-4e33-ad53-97d88bedc8d7">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems_7f2ccb71-5819-4332-a511-251e5dc10ca5" xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CashAndCashEquivalentsFairValueDisclosure_f42d69f9-a301-4b82-9afc-92a8b1cdc5bd" xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_CashAndCashEquivalentsFairValueDisclosure"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems_7f2ccb71-5819-4332-a511-251e5dc10ca5" xlink:to="loc_us-gaap_CashAndCashEquivalentsFairValueDisclosure_f42d69f9-a301-4b82-9afc-92a8b1cdc5bd" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AssetsFairValueDisclosure_3aa65611-3066-47f0-8f4b-43e00341612d" xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_AssetsFairValueDisclosure"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems_7f2ccb71-5819-4332-a511-251e5dc10ca5" xlink:to="loc_us-gaap_AssetsFairValueDisclosure_3aa65611-3066-47f0-8f4b-43e00341612d" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LiabilitiesFairValueDisclosure_b860497b-c582-4a42-b9d0-50c00db53853" xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_LiabilitiesFairValueDisclosure"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems_7f2ccb71-5819-4332-a511-251e5dc10ca5" xlink:to="loc_us-gaap_LiabilitiesFairValueDisclosure_b860497b-c582-4a42-b9d0-50c00db53853" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable_362c97f6-9dca-475f-b832-84031b8958f0" xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems_7f2ccb71-5819-4332-a511-251e5dc10ca5" xlink:to="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable_362c97f6-9dca-475f-b832-84031b8958f0" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueByMeasurementFrequencyAxis_6199423e-ea72-4109-bb01-cc80cbbaccb0" xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_FairValueByMeasurementFrequencyAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable_362c97f6-9dca-475f-b832-84031b8958f0" xlink:to="loc_us-gaap_FairValueByMeasurementFrequencyAxis_6199423e-ea72-4109-bb01-cc80cbbaccb0" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueMeasurementFrequencyDomain_6199423e-ea72-4109-bb01-cc80cbbaccb0_default" xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_FairValueMeasurementFrequencyDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_FairValueByMeasurementFrequencyAxis_6199423e-ea72-4109-bb01-cc80cbbaccb0" xlink:to="loc_us-gaap_FairValueMeasurementFrequencyDomain_6199423e-ea72-4109-bb01-cc80cbbaccb0_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueMeasurementFrequencyDomain_ca70520b-253e-4248-b7f1-554060ce967a" xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_FairValueMeasurementFrequencyDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_FairValueByMeasurementFrequencyAxis_6199423e-ea72-4109-bb01-cc80cbbaccb0" xlink:to="loc_us-gaap_FairValueMeasurementFrequencyDomain_ca70520b-253e-4248-b7f1-554060ce967a" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueMeasurementsRecurringMember_f98d0c0d-7d09-4201-95c6-00f3de33fd87" xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_FairValueMeasurementsRecurringMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueMeasurementFrequencyDomain_ca70520b-253e-4248-b7f1-554060ce967a" xlink:to="loc_us-gaap_FairValueMeasurementsRecurringMember_f98d0c0d-7d09-4201-95c6-00f3de33fd87" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueByFairValueHierarchyLevelAxis_4df42210-f2b7-4292-ae5c-218f9b2eaa42" xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_FairValueByFairValueHierarchyLevelAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable_362c97f6-9dca-475f-b832-84031b8958f0" xlink:to="loc_us-gaap_FairValueByFairValueHierarchyLevelAxis_4df42210-f2b7-4292-ae5c-218f9b2eaa42" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_4df42210-f2b7-4292-ae5c-218f9b2eaa42_default" xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_FairValueMeasurementsFairValueHierarchyDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_FairValueByFairValueHierarchyLevelAxis_4df42210-f2b7-4292-ae5c-218f9b2eaa42" xlink:to="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_4df42210-f2b7-4292-ae5c-218f9b2eaa42_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_146f1d19-0436-4a13-8617-ade81d92a522" xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_FairValueMeasurementsFairValueHierarchyDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_FairValueByFairValueHierarchyLevelAxis_4df42210-f2b7-4292-ae5c-218f9b2eaa42" xlink:to="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_146f1d19-0436-4a13-8617-ade81d92a522" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueInputsLevel1Member_63911910-b67e-4ee4-953a-006d452137ce" xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_FairValueInputsLevel1Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_146f1d19-0436-4a13-8617-ade81d92a522" xlink:to="loc_us-gaap_FairValueInputsLevel1Member_63911910-b67e-4ee4-953a-006d452137ce" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueInputsLevel2Member_418bd628-df73-4eb6-baf7-ac9b1e723ddc" xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_FairValueInputsLevel2Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_146f1d19-0436-4a13-8617-ade81d92a522" xlink:to="loc_us-gaap_FairValueInputsLevel2Member_418bd628-df73-4eb6-baf7-ac9b1e723ddc" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueInputsLevel3Member_ab4590b9-c6ac-442b-969d-1cd70dec9208" xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_FairValueInputsLevel3Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_146f1d19-0436-4a13-8617-ade81d92a522" xlink:to="loc_us-gaap_FairValueInputsLevel3Member_ab4590b9-c6ac-442b-969d-1cd70dec9208" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueByAssetClassAxis_ecc2d9a4-03d0-4242-949a-b3c4e0250007" xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_FairValueByAssetClassAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable_362c97f6-9dca-475f-b832-84031b8958f0" xlink:to="loc_us-gaap_FairValueByAssetClassAxis_ecc2d9a4-03d0-4242-949a-b3c4e0250007" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationByAssetClassDomain_ecc2d9a4-03d0-4242-949a-b3c4e0250007_default" xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationByAssetClassDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_FairValueByAssetClassAxis_ecc2d9a4-03d0-4242-949a-b3c4e0250007" xlink:to="loc_us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationByAssetClassDomain_ecc2d9a4-03d0-4242-949a-b3c4e0250007_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationByAssetClassDomain_12e9da6e-a414-450f-8cc1-e5dc68367e8b" xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationByAssetClassDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_FairValueByAssetClassAxis_ecc2d9a4-03d0-4242-949a-b3c4e0250007" xlink:to="loc_us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationByAssetClassDomain_12e9da6e-a414-450f-8cc1-e5dc68367e8b" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_MoneyMarketFundsMember_403a6d68-2917-479b-840e-9f094f60af77" xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_MoneyMarketFundsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationByAssetClassDomain_12e9da6e-a414-450f-8cc1-e5dc68367e8b" xlink:to="loc_us-gaap_MoneyMarketFundsMember_403a6d68-2917-479b-840e-9f094f60af77" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommodityMember_1e83daaf-bcbf-4767-9d8a-cd9d442a2bb4" xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_CommodityMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationByAssetClassDomain_12e9da6e-a414-450f-8cc1-e5dc68367e8b" xlink:to="loc_us-gaap_CommodityMember_1e83daaf-bcbf-4767-9d8a-cd9d442a2bb4" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ForeignExchangeMember_7c3123e5-ffd2-41a6-8802-a018e9d64388" xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_ForeignExchangeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationByAssetClassDomain_12e9da6e-a414-450f-8cc1-e5dc68367e8b" xlink:to="loc_us-gaap_ForeignExchangeMember_7c3123e5-ffd2-41a6-8802-a018e9d64388" xlink:type="arc" order="2"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.cmc.com/role/FAIRVALUEFinancialAssetsandLiabilitiesNotRequiredtoBeMeasuredatFairValueDetails" xlink:type="simple" xlink:href="cmc-20200229.xsd#FAIRVALUEFinancialAssetsandLiabilitiesNotRequiredtoBeMeasuredatFairValueDetails"/>
  <link:definitionLink xlink:role="http://www.cmc.com/role/FAIRVALUEFinancialAssetsandLiabilitiesNotRequiredtoBeMeasuredatFairValueDetails" xlink:type="extended" id="ief2169c4650e4430888c59e5eed76517_bef0a061-a163-4099-a802-63cbfcd68851">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueInvestmentsEntitiesThatCalculateNetAssetValuePerShareLineItems_0b9511dd-a50b-4c61-ad2c-99f4db668807" xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_FairValueInvestmentsEntitiesThatCalculateNetAssetValuePerShareLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtAndCapitalLeaseObligations_e3ac9b36-5093-4439-b2ba-3e47e61ede92" xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_DebtAndCapitalLeaseObligations"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueInvestmentsEntitiesThatCalculateNetAssetValuePerShareLineItems_0b9511dd-a50b-4c61-ad2c-99f4db668807" xlink:to="loc_us-gaap_DebtAndCapitalLeaseObligations_e3ac9b36-5093-4439-b2ba-3e47e61ede92" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueInvestmentsEntitiesThatCalculateNetAssetValuePerShareTable_2bfada42-825a-406d-b927-a7407e415bff" xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_FairValueInvestmentsEntitiesThatCalculateNetAssetValuePerShareTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_FairValueInvestmentsEntitiesThatCalculateNetAssetValuePerShareLineItems_0b9511dd-a50b-4c61-ad2c-99f4db668807" xlink:to="loc_us-gaap_FairValueInvestmentsEntitiesThatCalculateNetAssetValuePerShareTable_2bfada42-825a-406d-b927-a7407e415bff" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CreditFacilityAxis_4dd21e7b-ff35-40c2-9453-5ce7e6b012d3" xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_CreditFacilityAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_FairValueInvestmentsEntitiesThatCalculateNetAssetValuePerShareTable_2bfada42-825a-406d-b927-a7407e415bff" xlink:to="loc_us-gaap_CreditFacilityAxis_4dd21e7b-ff35-40c2-9453-5ce7e6b012d3" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CreditFacilityDomain_4dd21e7b-ff35-40c2-9453-5ce7e6b012d3_default" xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_CreditFacilityDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_CreditFacilityAxis_4dd21e7b-ff35-40c2-9453-5ce7e6b012d3" xlink:to="loc_us-gaap_CreditFacilityDomain_4dd21e7b-ff35-40c2-9453-5ce7e6b012d3_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CreditFacilityDomain_f595bb5b-b7d8-4461-b965-cf6a7685d158" xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_CreditFacilityDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_CreditFacilityAxis_4dd21e7b-ff35-40c2-9453-5ce7e6b012d3" xlink:to="loc_us-gaap_CreditFacilityDomain_f595bb5b-b7d8-4461-b965-cf6a7685d158" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RevolvingCreditFacilityMember_24fa3283-c344-49a1-bdd8-902260485bf1" xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_RevolvingCreditFacilityMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_CreditFacilityDomain_f595bb5b-b7d8-4461-b965-cf6a7685d158" xlink:to="loc_us-gaap_RevolvingCreditFacilityMember_24fa3283-c344-49a1-bdd8-902260485bf1" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongtermDebtTypeAxis_262afde7-0ea1-47d3-a335-4c8057ae4c6d" xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_LongtermDebtTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_FairValueInvestmentsEntitiesThatCalculateNetAssetValuePerShareTable_2bfada42-825a-406d-b927-a7407e415bff" xlink:to="loc_us-gaap_LongtermDebtTypeAxis_262afde7-0ea1-47d3-a335-4c8057ae4c6d" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongtermDebtTypeDomain_262afde7-0ea1-47d3-a335-4c8057ae4c6d_default" xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_LongtermDebtTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_LongtermDebtTypeAxis_262afde7-0ea1-47d3-a335-4c8057ae4c6d" xlink:to="loc_us-gaap_LongtermDebtTypeDomain_262afde7-0ea1-47d3-a335-4c8057ae4c6d_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongtermDebtTypeDomain_76462dc5-5252-4c53-9d2b-fe7767d9de7a" xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_LongtermDebtTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_LongtermDebtTypeAxis_262afde7-0ea1-47d3-a335-4c8057ae4c6d" xlink:to="loc_us-gaap_LongtermDebtTypeDomain_76462dc5-5252-4c53-9d2b-fe7767d9de7a" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_cmc_A300MillionNotesat5.375dueJuly2027Member_78032613-67bf-42dd-8e6c-e5bff9ae49e1" xlink:href="cmc-20200229.xsd#cmc_A300MillionNotesat5.375dueJuly2027Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LongtermDebtTypeDomain_76462dc5-5252-4c53-9d2b-fe7767d9de7a" xlink:to="loc_cmc_A300MillionNotesat5.375dueJuly2027Member_78032613-67bf-42dd-8e6c-e5bff9ae49e1" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_cmc_A350millionnotesat5.75dueApril2026Member_3b00b13b-40ec-47aa-993c-ca493f5297cd" xlink:href="cmc-20200229.xsd#cmc_A350millionnotesat5.75dueApril2026Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LongtermDebtTypeDomain_76462dc5-5252-4c53-9d2b-fe7767d9de7a" xlink:to="loc_cmc_A350millionnotesat5.75dueApril2026Member_3b00b13b-40ec-47aa-993c-ca493f5297cd" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_cmc_A330MillionNotesAt4875DueMay2023Member_97a02d41-3b67-4439-892a-43b0cf7eadff" xlink:href="cmc-20200229.xsd#cmc_A330MillionNotesAt4875DueMay2023Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LongtermDebtTypeDomain_76462dc5-5252-4c53-9d2b-fe7767d9de7a" xlink:to="loc_cmc_A330MillionNotesAt4875DueMay2023Member_97a02d41-3b67-4439-892a-43b0cf7eadff" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_MediumTermNotesMember_26cc8ee6-ed97-423f-9198-de4ce803fb30" xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_MediumTermNotesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LongtermDebtTypeDomain_76462dc5-5252-4c53-9d2b-fe7767d9de7a" xlink:to="loc_us-gaap_MediumTermNotesMember_26cc8ee6-ed97-423f-9198-de4ce803fb30" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_cmc_PolandCreditFacilitiesMember_9f78eabf-83a2-416d-9328-1a99590d6a50" xlink:href="cmc-20200229.xsd#cmc_PolandCreditFacilitiesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LongtermDebtTypeDomain_76462dc5-5252-4c53-9d2b-fe7767d9de7a" xlink:to="loc_cmc_PolandCreditFacilitiesMember_9f78eabf-83a2-416d-9328-1a99590d6a50" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShortTermDebtMember_bcf878c0-9111-40fc-9251-f9da61393452" xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_ShortTermDebtMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LongtermDebtTypeDomain_76462dc5-5252-4c53-9d2b-fe7767d9de7a" xlink:to="loc_us-gaap_ShortTermDebtMember_bcf878c0-9111-40fc-9251-f9da61393452" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueByFairValueHierarchyLevelAxis_537bc8fa-a9c7-45aa-a94b-89c8760211d2" xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_FairValueByFairValueHierarchyLevelAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_FairValueInvestmentsEntitiesThatCalculateNetAssetValuePerShareTable_2bfada42-825a-406d-b927-a7407e415bff" xlink:to="loc_us-gaap_FairValueByFairValueHierarchyLevelAxis_537bc8fa-a9c7-45aa-a94b-89c8760211d2" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_537bc8fa-a9c7-45aa-a94b-89c8760211d2_default" xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_FairValueMeasurementsFairValueHierarchyDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_FairValueByFairValueHierarchyLevelAxis_537bc8fa-a9c7-45aa-a94b-89c8760211d2" xlink:to="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_537bc8fa-a9c7-45aa-a94b-89c8760211d2_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_7b0c0ec1-7b6a-4dba-91de-6dc79c4a19ce" xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_FairValueMeasurementsFairValueHierarchyDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_FairValueByFairValueHierarchyLevelAxis_537bc8fa-a9c7-45aa-a94b-89c8760211d2" xlink:to="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_7b0c0ec1-7b6a-4dba-91de-6dc79c4a19ce" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueInputsLevel2Member_8feec499-bfd3-4912-93fa-52f3de761e7c" xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_FairValueInputsLevel2Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_7b0c0ec1-7b6a-4dba-91de-6dc79c4a19ce" xlink:to="loc_us-gaap_FairValueInputsLevel2Member_8feec499-bfd3-4912-93fa-52f3de761e7c" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueByMeasurementBasisAxis_42c6c754-9cfb-4125-bc27-ff8fdfdeaf6a" xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_FairValueByMeasurementBasisAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_FairValueInvestmentsEntitiesThatCalculateNetAssetValuePerShareTable_2bfada42-825a-406d-b927-a7407e415bff" xlink:to="loc_us-gaap_FairValueByMeasurementBasisAxis_42c6c754-9cfb-4125-bc27-ff8fdfdeaf6a" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PortionAtFairValueFairValueDisclosureMember_42c6c754-9cfb-4125-bc27-ff8fdfdeaf6a_default" xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_PortionAtFairValueFairValueDisclosureMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_FairValueByMeasurementBasisAxis_42c6c754-9cfb-4125-bc27-ff8fdfdeaf6a" xlink:to="loc_us-gaap_PortionAtFairValueFairValueDisclosureMember_42c6c754-9cfb-4125-bc27-ff8fdfdeaf6a_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueDisclosureItemAmountsDomain_87361923-2ad7-4731-a090-f524a6d772bb" xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_FairValueDisclosureItemAmountsDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_FairValueByMeasurementBasisAxis_42c6c754-9cfb-4125-bc27-ff8fdfdeaf6a" xlink:to="loc_us-gaap_FairValueDisclosureItemAmountsDomain_87361923-2ad7-4731-a090-f524a6d772bb" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PortionAtFairValueFairValueDisclosureMember_0e96a9bb-6223-47f1-b201-0147180d47b2" xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_PortionAtFairValueFairValueDisclosureMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueDisclosureItemAmountsDomain_87361923-2ad7-4731-a090-f524a6d772bb" xlink:to="loc_us-gaap_PortionAtFairValueFairValueDisclosureMember_0e96a9bb-6223-47f1-b201-0147180d47b2" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EstimateOfFairValueFairValueDisclosureMember_f65fa838-4bc1-4986-a67e-ecd656dde21b" xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_EstimateOfFairValueFairValueDisclosureMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PortionAtFairValueFairValueDisclosureMember_0e96a9bb-6223-47f1-b201-0147180d47b2" xlink:to="loc_us-gaap_EstimateOfFairValueFairValueDisclosureMember_f65fa838-4bc1-4986-a67e-ecd656dde21b" xlink:type="arc" order="1"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.cmc.com/role/STOCKBASEDCOMPENSATIONPLANS" xlink:type="simple" xlink:href="cmc-20200229.xsd#STOCKBASEDCOMPENSATIONPLANS"/>
  <link:definitionLink xlink:role="http://www.cmc.com/role/STOCKBASEDCOMPENSATIONPLANS" xlink:type="extended" id="idc1041cfcce64971a39707663a7638a1_b74106d9-358a-4e9d-82c5-2711f904c500"/>
  <link:roleRef roleURI="http://www.cmc.com/role/STOCKBASEDCOMPENSATIONPLANSTables" xlink:type="simple" xlink:href="cmc-20200229.xsd#STOCKBASEDCOMPENSATIONPLANSTables"/>
  <link:definitionLink xlink:role="http://www.cmc.com/role/STOCKBASEDCOMPENSATIONPLANSTables" xlink:type="extended" id="i66da7f54788f4b068195d2b8d6cab3c2_19a5b54c-06e0-4de3-b022-22fed31fba17"/>
  <link:roleRef roleURI="http://www.cmc.com/role/STOCKBASEDCOMPENSATIONPLANSNarrativeDetails" xlink:type="simple" xlink:href="cmc-20200229.xsd#STOCKBASEDCOMPENSATIONPLANSNarrativeDetails"/>
  <link:definitionLink xlink:role="http://www.cmc.com/role/STOCKBASEDCOMPENSATIONPLANSNarrativeDetails" xlink:type="extended" id="i25fcb997f0784a9cb55581bfedbb12cf_2446867f-c630-419f-98fd-e9677f865654">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_71166f7d-c15a-4420-b71d-9c67c7acb01e" xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardAwardVestingPeriod1_2e21fac5-e65d-4d4e-9fb9-ad050cf97860" xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardAwardVestingPeriod1"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_71166f7d-c15a-4420-b71d-9c67c7acb01e" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardAwardVestingPeriod1_2e21fac5-e65d-4d4e-9fb9-ad050cf97860" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriod_b94e7e44-48e6-43fb-b79e-521e5889af82" xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriod"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_71166f7d-c15a-4420-b71d-9c67c7acb01e" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriod_b94e7e44-48e6-43fb-b79e-521e5889af82" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriodWeightedAverageGrantDateFairValue_5ca196d5-573b-4136-a7e8-2edabe61e11a" xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriodWeightedAverageGrantDateFairValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_71166f7d-c15a-4420-b71d-9c67c7acb01e" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriodWeightedAverageGrantDateFairValue_5ca196d5-573b-4136-a7e8-2edabe61e11a" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedNumber_cc3a0139-1b88-429a-944b-946d2709a3aa" xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedNumber"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_71166f7d-c15a-4420-b71d-9c67c7acb01e" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedNumber_cc3a0139-1b88-429a-944b-946d2709a3aa" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_cmc_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquivalentSharesExpectedToVest_78d32f1c-70f8-4146-b8ff-88863ce16690" xlink:href="cmc-20200229.xsd#cmc_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquivalentSharesExpectedToVest"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_71166f7d-c15a-4420-b71d-9c67c7acb01e" xlink:to="loc_cmc_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquivalentSharesExpectedToVest_78d32f1c-70f8-4146-b8ff-88863ce16690" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AllocatedShareBasedCompensationExpense_4c03e0f8-4399-43ca-ae4a-052011d579a6" xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_AllocatedShareBasedCompensationExpense"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_71166f7d-c15a-4420-b71d-9c67c7acb01e" xlink:to="loc_us-gaap_AllocatedShareBasedCompensationExpense_4c03e0f8-4399-43ca-ae4a-052011d579a6" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_85be95ef-f4d0-4efb-aa8b-9fa01cf032bd" xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_71166f7d-c15a-4420-b71d-9c67c7acb01e" xlink:to="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_85be95ef-f4d0-4efb-aa8b-9fa01cf032bd" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AwardDateAxis_536f73b4-b67d-4559-b029-ef1cc916ef13" xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_AwardDateAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_85be95ef-f4d0-4efb-aa8b-9fa01cf032bd" xlink:to="loc_us-gaap_AwardDateAxis_536f73b4-b67d-4559-b029-ef1cc916ef13" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AwardDateDomain_536f73b4-b67d-4559-b029-ef1cc916ef13_default" xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_AwardDateDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_AwardDateAxis_536f73b4-b67d-4559-b029-ef1cc916ef13" xlink:to="loc_us-gaap_AwardDateDomain_536f73b4-b67d-4559-b029-ef1cc916ef13_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AwardDateDomain_a0b95c43-2788-40b0-99c7-ee0f957f576e" xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_AwardDateDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_AwardDateAxis_536f73b4-b67d-4559-b029-ef1cc916ef13" xlink:to="loc_us-gaap_AwardDateDomain_a0b95c43-2788-40b0-99c7-ee0f957f576e" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_cmc_Fiscal2020Member_4050d13a-920e-4fec-b4b4-a56db1a531c4" xlink:href="cmc-20200229.xsd#cmc_Fiscal2020Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AwardDateDomain_a0b95c43-2788-40b0-99c7-ee0f957f576e" xlink:to="loc_cmc_Fiscal2020Member_4050d13a-920e-4fec-b4b4-a56db1a531c4" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AwardTypeAxis_4827e211-c71e-484a-a178-5bfb13c276f4" xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_AwardTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_85be95ef-f4d0-4efb-aa8b-9fa01cf032bd" xlink:to="loc_us-gaap_AwardTypeAxis_4827e211-c71e-484a-a178-5bfb13c276f4" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_4827e211-c71e-484a-a178-5bfb13c276f4_default" xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_AwardTypeAxis_4827e211-c71e-484a-a178-5bfb13c276f4" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_4827e211-c71e-484a-a178-5bfb13c276f4_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_942611a8-2f1c-4ce3-8cd7-98b5befba36b" xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_AwardTypeAxis_4827e211-c71e-484a-a178-5bfb13c276f4" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_942611a8-2f1c-4ce3-8cd7-98b5befba36b" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RestrictedStockUnitsRSUMember_9873333d-d738-4e17-910b-525fd3456029" xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_RestrictedStockUnitsRSUMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_942611a8-2f1c-4ce3-8cd7-98b5befba36b" xlink:to="loc_us-gaap_RestrictedStockUnitsRSUMember_9873333d-d738-4e17-910b-525fd3456029" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_cmc_PerformanceStockUnitsPsuMember_d4249731-ece3-43ad-a520-05ff46ee5c1d" xlink:href="cmc-20200229.xsd#cmc_PerformanceStockUnitsPsuMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_942611a8-2f1c-4ce3-8cd7-98b5befba36b" xlink:to="loc_cmc_PerformanceStockUnitsPsuMember_d4249731-ece3-43ad-a520-05ff46ee5c1d" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_cmc_RSUsAndPSUsMember_0e9b4a63-7c27-4608-8b25-54fc49c3b26f" xlink:href="cmc-20200229.xsd#cmc_RSUsAndPSUsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_942611a8-2f1c-4ce3-8cd7-98b5befba36b" xlink:to="loc_cmc_RSUsAndPSUsMember_0e9b4a63-7c27-4608-8b25-54fc49c3b26f" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PhantomShareUnitsPSUsMember_bdba86fa-a5d4-4dea-9a80-55a48e3bec28" xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_PhantomShareUnitsPSUsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_942611a8-2f1c-4ce3-8cd7-98b5befba36b" xlink:to="loc_us-gaap_PhantomShareUnitsPSUsMember_bdba86fa-a5d4-4dea-9a80-55a48e3bec28" xlink:type="arc" order="3"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.cmc.com/role/STOCKHOLDERSEQUITYANDEARNINGSPERSHARE" xlink:type="simple" xlink:href="cmc-20200229.xsd#STOCKHOLDERSEQUITYANDEARNINGSPERSHARE"/>
  <link:definitionLink xlink:role="http://www.cmc.com/role/STOCKHOLDERSEQUITYANDEARNINGSPERSHARE" xlink:type="extended" id="i3852f964ddd14cc1ad57b535e1ed1816_3f215cff-3dce-4ee4-923e-92a73e782a87"/>
  <link:roleRef roleURI="http://www.cmc.com/role/STOCKHOLDERSEQUITYANDEARNINGSPERSHARETables" xlink:type="simple" xlink:href="cmc-20200229.xsd#STOCKHOLDERSEQUITYANDEARNINGSPERSHARETables"/>
  <link:definitionLink xlink:role="http://www.cmc.com/role/STOCKHOLDERSEQUITYANDEARNINGSPERSHARETables" xlink:type="extended" id="i43e836e2c10b4060952858dd0e5181f1_84d11af8-ae2e-4ed8-847a-6745d67e1544"/>
  <link:roleRef roleURI="http://www.cmc.com/role/STOCKHOLDERSEQUITYANDEARNINGSPERSHARENarrativeDetails" xlink:type="simple" xlink:href="cmc-20200229.xsd#STOCKHOLDERSEQUITYANDEARNINGSPERSHARENarrativeDetails"/>
  <link:definitionLink xlink:role="http://www.cmc.com/role/STOCKHOLDERSEQUITYANDEARNINGSPERSHARENarrativeDetails" xlink:type="extended" id="i660ee0ab689a40bc9e05c15f2526711d_9af91708-9030-4d9e-9f2e-ad6f5db87531"/>
  <link:roleRef roleURI="http://www.cmc.com/role/STOCKHOLDERSEQUITYANDEARNINGSPERSHARECalculationsoftheBasicandDilutedEarningsPerShareDetails" xlink:type="simple" xlink:href="cmc-20200229.xsd#STOCKHOLDERSEQUITYANDEARNINGSPERSHARECalculationsoftheBasicandDilutedEarningsPerShareDetails"/>
  <link:definitionLink xlink:role="http://www.cmc.com/role/STOCKHOLDERSEQUITYANDEARNINGSPERSHARECalculationsoftheBasicandDilutedEarningsPerShareDetails" xlink:type="extended" id="if12788ae21e54523b4d3de0c988a98d4_204e9f0c-fa8f-4378-b9c9-508e70ac773c"/>
  <link:roleRef roleURI="http://www.cmc.com/role/COMMITMENTSANDCONTINGENCIES" xlink:type="simple" xlink:href="cmc-20200229.xsd#COMMITMENTSANDCONTINGENCIES"/>
  <link:definitionLink xlink:role="http://www.cmc.com/role/COMMITMENTSANDCONTINGENCIES" xlink:type="extended" id="i38b9d700619f4881976fc59a2df379e1_a0295673-6c95-424e-a1b2-6455ff40dbe3"/>
  <link:roleRef roleURI="http://www.cmc.com/role/COMMITMENTSANDCONTINGENCIESNarrativeDetails" xlink:type="simple" xlink:href="cmc-20200229.xsd#COMMITMENTSANDCONTINGENCIESNarrativeDetails"/>
  <link:definitionLink xlink:role="http://www.cmc.com/role/COMMITMENTSANDCONTINGENCIESNarrativeDetails" xlink:type="extended" id="i39af707d9ce94173ba859e304e374cdc_76340b01-38a3-41bf-9a45-52cf2c358b64">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LossContingenciesLineItems_545648a6-cc1e-4257-8b11-3ecf6be1f228" xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_LossContingenciesLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AccrualForEnvironmentalLossContingencies_dbb3e90e-854c-49c9-af23-77b6f0040b04" xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_AccrualForEnvironmentalLossContingencies"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LossContingenciesLineItems_545648a6-cc1e-4257-8b11-3ecf6be1f228" xlink:to="loc_us-gaap_AccrualForEnvironmentalLossContingencies_dbb3e90e-854c-49c9-af23-77b6f0040b04" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AccruedEnvironmentalLossContingenciesNoncurrent_a8c1c201-2604-4521-a187-7e226f8abf02" xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_AccruedEnvironmentalLossContingenciesNoncurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LossContingenciesLineItems_545648a6-cc1e-4257-8b11-3ecf6be1f228" xlink:to="loc_us-gaap_AccruedEnvironmentalLossContingenciesNoncurrent_a8c1c201-2604-4521-a187-7e226f8abf02" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LossContingenciesTable_b488241f-102b-4ce4-a841-231a3d29c190" xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_LossContingenciesTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_LossContingenciesLineItems_545648a6-cc1e-4257-8b11-3ecf6be1f228" xlink:to="loc_us-gaap_LossContingenciesTable_b488241f-102b-4ce4-a841-231a3d29c190" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LossContingenciesByNatureOfContingencyAxis_f4170d5d-09b9-4e48-a2e8-0cee827d6006" xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_LossContingenciesByNatureOfContingencyAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_LossContingenciesTable_b488241f-102b-4ce4-a841-231a3d29c190" xlink:to="loc_us-gaap_LossContingenciesByNatureOfContingencyAxis_f4170d5d-09b9-4e48-a2e8-0cee827d6006" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LossContingencyNatureDomain_f4170d5d-09b9-4e48-a2e8-0cee827d6006_default" xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_LossContingencyNatureDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_LossContingenciesByNatureOfContingencyAxis_f4170d5d-09b9-4e48-a2e8-0cee827d6006" xlink:to="loc_us-gaap_LossContingencyNatureDomain_f4170d5d-09b9-4e48-a2e8-0cee827d6006_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LossContingencyNatureDomain_99b14ef8-6ed8-434b-9df7-e5e969fe7832" xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_LossContingencyNatureDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_LossContingenciesByNatureOfContingencyAxis_f4170d5d-09b9-4e48-a2e8-0cee827d6006" xlink:to="loc_us-gaap_LossContingencyNatureDomain_99b14ef8-6ed8-434b-9df7-e5e969fe7832" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_cmc_CerclaSitesMember_e1b00d48-1902-42a5-9719-249853977198" xlink:href="cmc-20200229.xsd#cmc_CerclaSitesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LossContingencyNatureDomain_99b14ef8-6ed8-434b-9df7-e5e969fe7832" xlink:to="loc_cmc_CerclaSitesMember_e1b00d48-1902-42a5-9719-249853977198" xlink:type="arc" order="0"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.cmc.com/role/BUSINESSSEGMENTS" xlink:type="simple" xlink:href="cmc-20200229.xsd#BUSINESSSEGMENTS"/>
  <link:definitionLink xlink:role="http://www.cmc.com/role/BUSINESSSEGMENTS" xlink:type="extended" id="i23e6fd461a3747829ce3724a2ec4edf5_1b80287a-e76e-4a6a-bac1-8ed6326f6819"/>
  <link:roleRef roleURI="http://www.cmc.com/role/BUSINESSSEGMENTSTables" xlink:type="simple" xlink:href="cmc-20200229.xsd#BUSINESSSEGMENTSTables"/>
  <link:definitionLink xlink:role="http://www.cmc.com/role/BUSINESSSEGMENTSTables" xlink:type="extended" id="i4fd9651ee44e4e889e3e1e8066e81ffd_801caee1-b131-406d-ab0c-e01ecff24652"/>
  <link:roleRef roleURI="http://www.cmc.com/role/BUSINESSSEGMENTSNarrativeDetails" xlink:type="simple" xlink:href="cmc-20200229.xsd#BUSINESSSEGMENTSNarrativeDetails"/>
  <link:definitionLink xlink:role="http://www.cmc.com/role/BUSINESSSEGMENTSNarrativeDetails" xlink:type="extended" id="ie631c156e2374ea288b93f8571839f91_aa124c0c-eeb0-4c45-9d83-4b145ce87cae"/>
  <link:roleRef roleURI="http://www.cmc.com/role/BUSINESSSEGMENTSSummaryofCertainFinancialInformationfromContinuingOperationsbyReportableSegmentDetails" xlink:type="simple" xlink:href="cmc-20200229.xsd#BUSINESSSEGMENTSSummaryofCertainFinancialInformationfromContinuingOperationsbyReportableSegmentDetails"/>
  <link:definitionLink xlink:role="http://www.cmc.com/role/BUSINESSSEGMENTSSummaryofCertainFinancialInformationfromContinuingOperationsbyReportableSegmentDetails" xlink:type="extended" id="i923a66363be44e75b49b9ade03b0f630_909a8662-fdaa-4e7a-92bb-4909fe71df49">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SegmentReportingInformationLineItems_f855dcb7-e32e-4220-a648-af3644742da1" xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_SegmentReportingInformationLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RevenueFromContractWithCustomerIncludingAssessedTax_57dc350d-f41d-426f-8b58-3c4e77432645" xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_RevenueFromContractWithCustomerIncludingAssessedTax"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_f855dcb7-e32e-4220-a648-af3644742da1" xlink:to="loc_us-gaap_RevenueFromContractWithCustomerIncludingAssessedTax_57dc350d-f41d-426f-8b58-3c4e77432645" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_cmc_AdjustedOperatingProfitLossFromContinuingOperation_1ec33a09-377e-4cb0-9d05-8170ff8b6862" xlink:href="cmc-20200229.xsd#cmc_AdjustedOperatingProfitLossFromContinuingOperation"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_f855dcb7-e32e-4220-a648-af3644742da1" xlink:to="loc_cmc_AdjustedOperatingProfitLossFromContinuingOperation_1ec33a09-377e-4cb0-9d05-8170ff8b6862" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_Assets_ee3d4473-8701-486b-976f-ff29a4314d33" xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_Assets"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_f855dcb7-e32e-4220-a648-af3644742da1" xlink:to="loc_us-gaap_Assets_ee3d4473-8701-486b-976f-ff29a4314d33" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfSegmentReportingInformationBySegmentTable_8d9bb714-0801-4d2f-b9a4-7b70a2ea0e68" xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_ScheduleOfSegmentReportingInformationBySegmentTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_f855dcb7-e32e-4220-a648-af3644742da1" xlink:to="loc_us-gaap_ScheduleOfSegmentReportingInformationBySegmentTable_8d9bb714-0801-4d2f-b9a4-7b70a2ea0e68" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidationItemsAxis_03a4956a-c1b1-4e8b-8eba-a96f29dd4ff0" xlink:href="http://xbrl.fasb.org/srt/2019/elts/srt-2019-01-31.xsd#srt_ConsolidationItemsAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfSegmentReportingInformationBySegmentTable_8d9bb714-0801-4d2f-b9a4-7b70a2ea0e68" xlink:to="loc_srt_ConsolidationItemsAxis_03a4956a-c1b1-4e8b-8eba-a96f29dd4ff0" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidationItemsDomain_03a4956a-c1b1-4e8b-8eba-a96f29dd4ff0_default" xlink:href="http://xbrl.fasb.org/srt/2019/elts/srt-2019-01-31.xsd#srt_ConsolidationItemsDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_ConsolidationItemsAxis_03a4956a-c1b1-4e8b-8eba-a96f29dd4ff0" xlink:to="loc_srt_ConsolidationItemsDomain_03a4956a-c1b1-4e8b-8eba-a96f29dd4ff0_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidationItemsDomain_eaac0037-51ad-4c7e-915d-d04603f18b25" xlink:href="http://xbrl.fasb.org/srt/2019/elts/srt-2019-01-31.xsd#srt_ConsolidationItemsDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_ConsolidationItemsAxis_03a4956a-c1b1-4e8b-8eba-a96f29dd4ff0" xlink:to="loc_srt_ConsolidationItemsDomain_eaac0037-51ad-4c7e-915d-d04603f18b25" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_MaterialReconcilingItemsMember_8a17b550-2823-4c2a-82ac-ea6f6002a553" xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_MaterialReconcilingItemsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ConsolidationItemsDomain_eaac0037-51ad-4c7e-915d-d04603f18b25" xlink:to="loc_us-gaap_MaterialReconcilingItemsMember_8a17b550-2823-4c2a-82ac-ea6f6002a553" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OperatingSegmentsMember_b0620561-ab1d-4fbf-8b3a-74e26b507476" xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_OperatingSegmentsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ConsolidationItemsDomain_eaac0037-51ad-4c7e-915d-d04603f18b25" xlink:to="loc_us-gaap_OperatingSegmentsMember_b0620561-ab1d-4fbf-8b3a-74e26b507476" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementBusinessSegmentsAxis_3ea895fd-7420-4ef3-9a68-7e0fb5575af3" xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_StatementBusinessSegmentsAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfSegmentReportingInformationBySegmentTable_8d9bb714-0801-4d2f-b9a4-7b70a2ea0e68" xlink:to="loc_us-gaap_StatementBusinessSegmentsAxis_3ea895fd-7420-4ef3-9a68-7e0fb5575af3" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SegmentDomain_3ea895fd-7420-4ef3-9a68-7e0fb5575af3_default" xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_SegmentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_StatementBusinessSegmentsAxis_3ea895fd-7420-4ef3-9a68-7e0fb5575af3" xlink:to="loc_us-gaap_SegmentDomain_3ea895fd-7420-4ef3-9a68-7e0fb5575af3_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SegmentDomain_2236c565-88a8-4be4-9a87-15eb1385e80a" xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_SegmentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_StatementBusinessSegmentsAxis_3ea895fd-7420-4ef3-9a68-7e0fb5575af3" xlink:to="loc_us-gaap_SegmentDomain_2236c565-88a8-4be4-9a87-15eb1385e80a" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SegmentContinuingOperationsMember_61b7a46a-8d4f-4e3c-8977-168395061fa9" xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_SegmentContinuingOperationsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentDomain_2236c565-88a8-4be4-9a87-15eb1385e80a" xlink:to="loc_us-gaap_SegmentContinuingOperationsMember_61b7a46a-8d4f-4e3c-8977-168395061fa9" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_cmc_AmericasRecyclingMember_dac37616-cd57-408f-ab8d-5990f92588dc" xlink:href="cmc-20200229.xsd#cmc_AmericasRecyclingMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentContinuingOperationsMember_61b7a46a-8d4f-4e3c-8977-168395061fa9" xlink:to="loc_cmc_AmericasRecyclingMember_dac37616-cd57-408f-ab8d-5990f92588dc" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_cmc_AmericasMillsMember_ed942de4-df8e-47ba-8fd9-f4698cd092d8" xlink:href="cmc-20200229.xsd#cmc_AmericasMillsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentContinuingOperationsMember_61b7a46a-8d4f-4e3c-8977-168395061fa9" xlink:to="loc_cmc_AmericasMillsMember_ed942de4-df8e-47ba-8fd9-f4698cd092d8" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_cmc_AmericasFabricationMember_686e7d86-8133-41d7-a688-a362354eea0f" xlink:href="cmc-20200229.xsd#cmc_AmericasFabricationMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentContinuingOperationsMember_61b7a46a-8d4f-4e3c-8977-168395061fa9" xlink:to="loc_cmc_AmericasFabricationMember_686e7d86-8133-41d7-a688-a362354eea0f" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_cmc_InternationalMillsMember_5f8da08a-0246-47f4-9168-8bdd54f0d01b" xlink:href="cmc-20200229.xsd#cmc_InternationalMillsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentContinuingOperationsMember_61b7a46a-8d4f-4e3c-8977-168395061fa9" xlink:to="loc_cmc_InternationalMillsMember_5f8da08a-0246-47f4-9168-8bdd54f0d01b" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CorporateMember_6a01c3b8-072a-4801-88e5-f6d459f9a6a0" xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_CorporateMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentContinuingOperationsMember_61b7a46a-8d4f-4e3c-8977-168395061fa9" xlink:to="loc_us-gaap_CorporateMember_6a01c3b8-072a-4801-88e5-f6d459f9a6a0" xlink:type="arc" order="5"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.cmc.com/role/BUSINESSSEGMENTSReconciliationsofEarningsfromContinuingOperationstoAdjustedOperatingProfitDetails" xlink:type="simple" xlink:href="cmc-20200229.xsd#BUSINESSSEGMENTSReconciliationsofEarningsfromContinuingOperationstoAdjustedOperatingProfitDetails"/>
  <link:definitionLink xlink:role="http://www.cmc.com/role/BUSINESSSEGMENTSReconciliationsofEarningsfromContinuingOperationstoAdjustedOperatingProfitDetails" xlink:type="extended" id="i598952b6ba9d4960b4e5023efd8bec85_fc35462c-afbc-4caf-bffe-9e39b2b543b2"/>
</link:linkbase>
