<?xml version="1.0" encoding="US-ASCII" standalone="no"?>
    <!-- Field: Doc-Info; Name: Generator; Value: GoFiler Complete; Version: 6.0b -->
    <!-- Field: Doc-Info; Name: VendorURI; Value: https://www.novaworks.com -->
    <!-- Field: Doc-Info; Name: Status; Value: 0x00000000 -->
<link:linkbase xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns:xlink="http://www.w3.org/1999/xlink" xmlns:link="http://www.xbrl.org/2003/linkbase" xmlns:xbrldt="http://xbrl.org/2005/xbrldt" xmlns:xbrli="http://www.xbrl.org/2003/instance" xsi:schemaLocation="http://www.xbrl.org/2003/linkbase http://www.xbrl.org/2003/xbrl-linkbase-2003-12-31.xsd">
    <link:roleRef roleURI="http://nanophase.com/role/Cover" xlink:href="nanx-20241231.xsd#Cover" xlink:type="simple" />
    <link:roleRef roleURI="http://nanophase.com/role/ConsolidatedBalanceSheets" xlink:href="nanx-20241231.xsd#ConsolidatedBalanceSheets" xlink:type="simple" />
    <link:roleRef roleURI="http://nanophase.com/role/ConsolidatedBalanceSheetsParenthetical" xlink:href="nanx-20241231.xsd#ConsolidatedBalanceSheetsParenthetical" xlink:type="simple" />
    <link:roleRef roleURI="http://nanophase.com/role/ConsolidatedStatementsOfOperations" xlink:href="nanx-20241231.xsd#ConsolidatedStatementsOfOperations" xlink:type="simple" />
    <link:roleRef roleURI="http://nanophase.com/role/ConsolidatedStatementsOfStockholdersEquity" xlink:href="nanx-20241231.xsd#ConsolidatedStatementsOfStockholdersEquity" xlink:type="simple" />
    <link:roleRef roleURI="http://nanophase.com/role/ConsolidatedStatementsOfCashFlows" xlink:href="nanx-20241231.xsd#ConsolidatedStatementsOfCashFlows" xlink:type="simple" />
    <link:roleRef roleURI="http://xbrl.sec.gov/cyd/role/CybersecurityRiskManagementAndStrategyDisclosure" xlink:href="https://xbrl.sec.gov/cyd/2024/cyd-2024.xsd#CybersecurityRiskManagementAndStrategyDisclosure" xlink:type="simple" />
    <link:roleRef roleURI="http://xbrl.sec.gov/cyd/role/MaterialCybersecurityIncidentDisclosure" xlink:href="https://xbrl.sec.gov/cyd/2024/cyd-2024.xsd#MaterialCybersecurityIncidentDisclosure" xlink:type="simple" />
    <link:roleRef roleURI="http://nanophase.com/role/RiskAssessmentAndStrategy" xlink:href="nanx-20241231.xsd#RiskAssessmentAndStrategy" xlink:type="simple" />
    <link:roleRef roleURI="http://nanophase.com/role/ManagementOversight" xlink:href="nanx-20241231.xsd#ManagementOversight" xlink:type="simple" />
    <link:roleRef roleURI="http://nanophase.com/role/DescriptionOfBusiness" xlink:href="nanx-20241231.xsd#DescriptionOfBusiness" xlink:type="simple" />
    <link:roleRef roleURI="http://nanophase.com/role/SummaryOfSignificantAccountingPolicies" xlink:href="nanx-20241231.xsd#SummaryOfSignificantAccountingPolicies" xlink:type="simple" />
    <link:roleRef roleURI="http://nanophase.com/role/RelatedPartyNotesAndLinesOfCredit" xlink:href="nanx-20241231.xsd#RelatedPartyNotesAndLinesOfCredit" xlink:type="simple" />
    <link:roleRef roleURI="http://nanophase.com/role/InventoriesNet" xlink:href="nanx-20241231.xsd#InventoriesNet" xlink:type="simple" />
    <link:roleRef roleURI="http://nanophase.com/role/EquipmentAndLeaseholdImprovements" xlink:href="nanx-20241231.xsd#EquipmentAndLeaseholdImprovements" xlink:type="simple" />
    <link:roleRef roleURI="http://nanophase.com/role/LeaseCommitments" xlink:href="nanx-20241231.xsd#LeaseCommitments" xlink:type="simple" />
    <link:roleRef roleURI="http://nanophase.com/role/AccruedExpenses" xlink:href="nanx-20241231.xsd#AccruedExpenses" xlink:type="simple" />
    <link:roleRef roleURI="http://nanophase.com/role/IncomeTaxes" xlink:href="nanx-20241231.xsd#IncomeTaxes" xlink:type="simple" />
    <link:roleRef roleURI="http://nanophase.com/role/CapitalStock" xlink:href="nanx-20241231.xsd#CapitalStock" xlink:type="simple" />
    <link:roleRef roleURI="http://nanophase.com/role/StockOptionsAndStockGrants" xlink:href="nanx-20241231.xsd#StockOptionsAndStockGrants" xlink:type="simple" />
    <link:roleRef roleURI="http://nanophase.com/role/KProfit-sharingPlan" xlink:href="nanx-20241231.xsd#KProfit-sharingPlan" xlink:type="simple" />
    <link:roleRef roleURI="http://nanophase.com/role/SignificantCustomers" xlink:href="nanx-20241231.xsd#SignificantCustomers" xlink:type="simple" />
    <link:roleRef roleURI="http://nanophase.com/role/BusinessSegmentationAndGeographicalDistribution" xlink:href="nanx-20241231.xsd#BusinessSegmentationAndGeographicalDistribution" xlink:type="simple" />
    <link:roleRef roleURI="http://nanophase.com/role/SubsequentEvent" xlink:href="nanx-20241231.xsd#SubsequentEvent" xlink:type="simple" />
    <link:roleRef roleURI="http://nanophase.com/role/SummaryOfSignificantAccountingPoliciesPolicies" xlink:href="nanx-20241231.xsd#SummaryOfSignificantAccountingPoliciesPolicies" xlink:type="simple" />
    <link:roleRef roleURI="http://nanophase.com/role/SummaryOfSignificantAccountingPoliciesTables" xlink:href="nanx-20241231.xsd#SummaryOfSignificantAccountingPoliciesTables" xlink:type="simple" />
    <link:roleRef roleURI="http://nanophase.com/role/RelatedPartyNotesAndLinesOfCreditTables" xlink:href="nanx-20241231.xsd#RelatedPartyNotesAndLinesOfCreditTables" xlink:type="simple" />
    <link:roleRef roleURI="http://nanophase.com/role/InventoriesNetTables" xlink:href="nanx-20241231.xsd#InventoriesNetTables" xlink:type="simple" />
    <link:roleRef roleURI="http://nanophase.com/role/EquipmentAndLeaseholdImprovementsTables" xlink:href="nanx-20241231.xsd#EquipmentAndLeaseholdImprovementsTables" xlink:type="simple" />
    <link:roleRef roleURI="http://nanophase.com/role/LeaseCommitmentsTables" xlink:href="nanx-20241231.xsd#LeaseCommitmentsTables" xlink:type="simple" />
    <link:roleRef roleURI="http://nanophase.com/role/AccruedExpensesTables" xlink:href="nanx-20241231.xsd#AccruedExpensesTables" xlink:type="simple" />
    <link:roleRef roleURI="http://nanophase.com/role/IncomeTaxesTables" xlink:href="nanx-20241231.xsd#IncomeTaxesTables" xlink:type="simple" />
    <link:roleRef roleURI="http://nanophase.com/role/StockOptionsAndStockGrantsTables" xlink:href="nanx-20241231.xsd#StockOptionsAndStockGrantsTables" xlink:type="simple" />
    <link:roleRef roleURI="http://nanophase.com/role/SignificantCustomersTables" xlink:href="nanx-20241231.xsd#SignificantCustomersTables" xlink:type="simple" />
    <link:roleRef roleURI="http://nanophase.com/role/BusinessSegmentationAndGeographicalDistributionTables" xlink:href="nanx-20241231.xsd#BusinessSegmentationAndGeographicalDistributionTables" xlink:type="simple" />
    <link:roleRef roleURI="http://nanophase.com/role/WeDetermineAllowanceForCreditLossesByIdentifyingTroubledAccountsAndByUsingHistoricalExperienceAppliedToAgingOfAccountsAsWellAsExpectedLossesBasedOnCurrentAndAnticipatedMacroeconomicEnvironment.Details" xlink:href="nanx-20241231.xsd#WeDetermineAllowanceForCreditLossesByIdentifyingTroubledAccountsAndByUsingHistoricalExperienceAppliedToAgingOfAccountsAsWellAsExpectedLossesBasedOnCurrentAndAnticipatedMacroeconomicEnvironment.Details" xlink:type="simple" />
    <link:roleRef roleURI="http://nanophase.com/role/ContractBalancesForYearsEndedDecember3120242023And2022AreAsFollowsDetails" xlink:href="nanx-20241231.xsd#ContractBalancesForYearsEndedDecember3120242023And2022AreAsFollowsDetails" xlink:type="simple" />
    <link:roleRef roleURI="http://nanophase.com/role/EarningsApplicableToCommonStockAndCommonStockSharesUsedInCalculationOfBasicAndDilutedEarningsPerShareAreAsFollowsDetails" xlink:href="nanx-20241231.xsd#EarningsApplicableToCommonStockAndCommonStockSharesUsedInCalculationOfBasicAndDilutedEarningsPerShareAreAsFollowsDetails" xlink:type="simple" />
    <link:roleRef roleURI="http://nanophase.com/role/SummaryOfSignificantAccountingPoliciesDetailsNarrative" xlink:href="nanx-20241231.xsd#SummaryOfSignificantAccountingPoliciesDetailsNarrative" xlink:type="simple" />
    <link:roleRef roleURI="http://nanophase.com/role/NotesAndLinesOfCreditConsistOfFollowingDetails" xlink:href="nanx-20241231.xsd#NotesAndLinesOfCreditConsistOfFollowingDetails" xlink:type="simple" />
    <link:roleRef roleURI="http://nanophase.com/role/RelatedPartyInterestExpenseConsistsOfFollowingDetails" xlink:href="nanx-20241231.xsd#RelatedPartyInterestExpenseConsistsOfFollowingDetails" xlink:type="simple" />
    <link:roleRef roleURI="http://nanophase.com/role/InventoriesConsistOfFollowingDetails" xlink:href="nanx-20241231.xsd#InventoriesConsistOfFollowingDetails" xlink:type="simple" />
    <link:roleRef roleURI="http://nanophase.com/role/EquipmentAndLeaseholdImprovementsConsistOfFollowingDetails" xlink:href="nanx-20241231.xsd#EquipmentAndLeaseholdImprovementsConsistOfFollowingDetails" xlink:type="simple" />
    <link:roleRef roleURI="http://nanophase.com/role/EquipmentAndLeaseholdImprovementsDetailsNarrative" xlink:href="nanx-20241231.xsd#EquipmentAndLeaseholdImprovementsDetailsNarrative" xlink:type="simple" />
    <link:roleRef roleURI="http://nanophase.com/role/QuantitativeInformationRegardingCompanysLeasesIsAsFollowsDetails" xlink:href="nanx-20241231.xsd#QuantitativeInformationRegardingCompanysLeasesIsAsFollowsDetails" xlink:type="simple" />
    <link:roleRef roleURI="http://nanophase.com/role/SupplementalCashFlowInformationRelatedToLeasesIsAsFollowsForYearsEndedDecember312024And2023Details" xlink:href="nanx-20241231.xsd#SupplementalCashFlowInformationRelatedToLeasesIsAsFollowsForYearsEndedDecember312024And2023Details" xlink:type="simple" />
    <link:roleRef roleURI="http://nanophase.com/role/FutureMaturitiesOfCompanysOperatingLeasesAsOfDecember312024AreAsFollowsDetails" xlink:href="nanx-20241231.xsd#FutureMaturitiesOfCompanysOperatingLeasesAsOfDecember312024AreAsFollowsDetails" xlink:type="simple" />
    <link:roleRef roleURI="http://nanophase.com/role/LeaseCommitmentsDetailsNarrative" xlink:href="nanx-20241231.xsd#LeaseCommitmentsDetailsNarrative" xlink:type="simple" />
    <link:roleRef roleURI="http://nanophase.com/role/AccruedExpensesConsistOfFollowingDetails" xlink:href="nanx-20241231.xsd#AccruedExpensesConsistOfFollowingDetails" xlink:type="simple" />
    <link:roleRef roleURI="http://nanophase.com/role/ReconciliationOfIncomeTaxBenefitToAmountComputedByApplyingFederalIncomeTaxRateToLossBeforeProvisionForIncomeTaxesAsOfDecember312024And2023IsAsFollowsDetails" xlink:href="nanx-20241231.xsd#ReconciliationOfIncomeTaxBenefitToAmountComputedByApplyingFederalIncomeTaxRateToLossBeforeProvisionForIncomeTaxesAsOfDecember312024And2023IsAsFollowsDetails" xlink:type="simple" />
    <link:roleRef roleURI="http://nanophase.com/role/DeferredIncomeTaxesReflectNetTaxEffectsOfTemporaryDifferencesBetweenCarryingAmountsOfAssetsAndLiabilitiesForFinancialReportingPurposesAndAmountsUsedForIncomeTaxPurposes.SignificantComponentsOfOurDeferredIncomeDetails" xlink:href="nanx-20241231.xsd#DeferredIncomeTaxesReflectNetTaxEffectsOfTemporaryDifferencesBetweenCarryingAmountsOfAssetsAndLiabilitiesForFinancialReportingPurposesAndAmountsUsedForIncomeTaxPurposes.SignificantComponentsOfOurDeferredIncomeDetails" xlink:type="simple" />
    <link:roleRef roleURI="http://nanophase.com/role/IncomeTaxesDetailsNarrative" xlink:href="nanx-20241231.xsd#IncomeTaxesDetailsNarrative" xlink:type="simple" />
    <link:roleRef roleURI="http://nanophase.com/role/CapitalStockDetailsNarrative" xlink:href="nanx-20241231.xsd#CapitalStockDetailsNarrative" xlink:type="simple" />
    <link:roleRef roleURI="http://nanophase.com/role/WeFollowAscTopic718Share-basedPaymentsInWhichCompensationExpenseIsRecognizedOnlyForShare-basedPaymentsExpectedToVest.Details" xlink:href="nanx-20241231.xsd#WeFollowAscTopic718Share-basedPaymentsInWhichCompensationExpenseIsRecognizedOnlyForShare-basedPaymentsExpectedToVest.Details" xlink:type="simple" />
    <link:roleRef roleURI="http://nanophase.com/role/FollowingTableIllustratesVariousAssumptionsUsedToCalculateBlack-scholesOptionPricingModelForOptionsGrantedForAllYearsPresentedDetails" xlink:href="nanx-20241231.xsd#FollowingTableIllustratesVariousAssumptionsUsedToCalculateBlack-scholesOptionPricingModelForOptionsGrantedForAllYearsPresentedDetails" xlink:type="simple" />
    <link:roleRef roleURI="http://nanophase.com/role/AdditionalDisclosuresForOptionsGrantedForAllYearsPresentedDetails" xlink:href="nanx-20241231.xsd#AdditionalDisclosuresForOptionsGrantedForAllYearsPresentedDetails" xlink:type="simple" />
    <link:roleRef roleURI="http://nanophase.com/role/FollowingTableSummarizesOptionActivityForOurEmployeesAndDirectorsDuringYearEndedDecember312024Details" xlink:href="nanx-20241231.xsd#FollowingTableSummarizesOptionActivityForOurEmployeesAndDirectorsDuringYearEndedDecember312024Details" xlink:type="simple" />
    <link:roleRef roleURI="http://nanophase.com/role/AggregateIntrinsicValueInTableAboveIsBasedOnOurClosingStockPriceOf2.26Details" xlink:href="nanx-20241231.xsd#AggregateIntrinsicValueInTableAboveIsBasedOnOurClosingStockPriceOf2.26Details" xlink:type="simple" />
    <link:roleRef roleURI="http://nanophase.com/role/StockOptionsAndStockGrantsDetailsNarrative" xlink:href="nanx-20241231.xsd#StockOptionsAndStockGrantsDetailsNarrative" xlink:type="simple" />
    <link:roleRef roleURI="http://nanophase.com/role/KProfit-sharingPlanDetailsNarrative" xlink:href="nanx-20241231.xsd#KProfit-sharingPlanDetailsNarrative" xlink:type="simple" />
    <link:roleRef roleURI="http://nanophase.com/role/RevenuesFromTheseThreeCustomersAsPercentageOfTotalCompanyRevenueWasApproximatelyDetails" xlink:href="nanx-20241231.xsd#RevenuesFromTheseThreeCustomersAsPercentageOfTotalCompanyRevenueWasApproximatelyDetails" xlink:type="simple" />
    <link:roleRef roleURI="http://nanophase.com/role/AccountsReceivableBalancesForTheseThreeCustomersAsPercentageOfTotalCompanyAccountsReceivableWasApproximatelyDetails" xlink:href="nanx-20241231.xsd#AccountsReceivableBalancesForTheseThreeCustomersAsPercentageOfTotalCompanyAccountsReceivableWasApproximatelyDetails" xlink:type="simple" />
    <link:roleRef roleURI="http://nanophase.com/role/SignificantCustomersDetailsNarrative" xlink:href="nanx-20241231.xsd#SignificantCustomersDetailsNarrative" xlink:type="simple" />
    <link:roleRef roleURI="http://nanophase.com/role/ChiefOperatingDecisionMakerUsesGrossProfitAndNetIncomeToEvaluateCompanyPerformanceAndInWhatWayToAllocateResources.SignificantSegmentExpensesWhichAreSameAsEntityAsWholeAreAsFollowsDetails" xlink:href="nanx-20241231.xsd#ChiefOperatingDecisionMakerUsesGrossProfitAndNetIncomeToEvaluateCompanyPerformanceAndInWhatWayToAllocateResources.SignificantSegmentExpensesWhichAreSameAsEntityAsWholeAreAsFollowsDetails" xlink:type="simple" />
    <link:roleRef roleURI="http://nanophase.com/role/RevenuesFor2024And2023ByCategoryAreAsFollowsDetails" xlink:href="nanx-20241231.xsd#RevenuesFor2024And2023ByCategoryAreAsFollowsDetails" xlink:type="simple" />
    <link:roleRef roleURI="http://nanophase.com/role/BusinessSegmentationAndGeographicalDistributionDetailsNarrative" xlink:href="nanx-20241231.xsd#BusinessSegmentationAndGeographicalDistributionDetailsNarrative" xlink:type="simple" />
    <link:roleRef roleURI="http://nanophase.com/role/SubsequentEventDetailsNarrative" xlink:href="nanx-20241231.xsd#SubsequentEventDetailsNarrative" xlink:type="simple" />
    <link:roleRef roleURI="http://xbrl.sec.gov/ecd/role/PvpDisclosureWithAdditionalMeasures" xlink:href="https://xbrl.sec.gov/ecd/2024/ecd-2024.xsd#PvpDisclosureWithAdditionalMeasures" xlink:type="simple" />
    <link:roleRef roleURI="http://xbrl.sec.gov/ecd/role/PvpTable" xlink:href="https://xbrl.sec.gov/ecd/2024/ecd-2024.xsd#PvpTable" xlink:type="simple" />
    <link:roleRef roleURI="http://xbrl.sec.gov/ecd/role/PvpAdjustmentsToCompensation" xlink:href="https://xbrl.sec.gov/ecd/2024/ecd-2024.xsd#PvpAdjustmentsToCompensation" xlink:type="simple" />
    <link:roleRef roleURI="http://xbrl.sec.gov/ecd/role/TabularListsByExecutiveCategory" xlink:href="https://xbrl.sec.gov/ecd/2024/ecd-2024.xsd#TabularListsByExecutiveCategory" xlink:type="simple" />
    <link:roleRef roleURI="http://xbrl.sec.gov/ecd/role/TabularListMeasures" xlink:href="https://xbrl.sec.gov/ecd/2024/ecd-2024.xsd#TabularListMeasures" xlink:type="simple" />
    <link:roleRef roleURI="http://xbrl.sec.gov/ecd/role/PvpMeasures" xlink:href="https://xbrl.sec.gov/ecd/2024/ecd-2024.xsd#PvpMeasures" xlink:type="simple" />
    <link:roleRef roleURI="http://xbrl.sec.gov/ecd/role/PvpExecutiveCategoriesOnly" xlink:href="https://xbrl.sec.gov/ecd/2024/ecd-2024.xsd#PvpExecutiveCategoriesOnly" xlink:type="simple" />
    <link:roleRef roleURI="http://xbrl.sec.gov/ecd/role/PvpAdjustmentsOnly" xlink:href="https://xbrl.sec.gov/ecd/2024/ecd-2024.xsd#PvpAdjustmentsOnly" xlink:type="simple" />
    <link:roleRef roleURI="http://xbrl.sec.gov/ecd/role/IndividualsOnly" xlink:href="https://xbrl.sec.gov/ecd/2024/ecd-2024.xsd#IndividualsOnly" xlink:type="simple" />
    <link:roleRef roleURI="http://xbrl.sec.gov/ecd/AwardTypeOnly" xlink:href="https://xbrl.sec.gov/ecd/2024/ecd-2024.xsd#AwardTypeOnly" xlink:type="simple" />
    <link:roleRef roleURI="http://xbrl.sec.gov/ecd/role/TradingArrangementsOnly" xlink:href="https://xbrl.sec.gov/ecd/2024/ecd-2024.xsd#TradingArrangmentsOnly" xlink:type="simple" />
    <link:roleRef roleURI="http://xbrl.sec.gov/ecd/role/ForgoneRecoveries" xlink:href="https://xbrl.sec.gov/ecd/2024/ecd-2024.xsd#ForgoneRecoveries" xlink:type="simple" />
    <link:roleRef roleURI="http://xbrl.sec.gov/ecd/role/OutstandingRecoveries" xlink:href="https://xbrl.sec.gov/ecd/2024/ecd-2024.xsd#OutstandingRecoveries" xlink:type="simple" />
    <link:roleRef roleURI="http://xbrl.sec.gov/ecd/role/AwardsCloseToMnpiDisc" xlink:href="https://xbrl.sec.gov/ecd/2024/ecd-2024.xsd#AwardsCloseToMnpiDisc" xlink:type="simple" />
    <link:roleRef roleURI="http://xbrl.sec.gov/ecd/role/InsiderTradingArrangementsByInd" xlink:href="https://xbrl.sec.gov/ecd/2024/ecd-2024.xsd#InsiderTradingArrangemenstByInd" xlink:type="simple" />
    <link:roleRef roleURI="http://xbrl.sec.gov/ecd/role/Defaults" xlink:href="https://xbrl.sec.gov/ecd/2024/ecd-2024.xsd#Defaults" xlink:type="simple" />
    <link:arcroleRef xlink:type="simple" xlink:href="http://www.xbrl.org/2005/xbrldt-2005.xsd#hypercube-dimension" arcroleURI="http://xbrl.org/int/dim/arcrole/hypercube-dimension" />
    <link:arcroleRef xlink:type="simple" xlink:href="http://www.xbrl.org/2005/xbrldt-2005.xsd#dimension-domain" arcroleURI="http://xbrl.org/int/dim/arcrole/dimension-domain" />
    <link:arcroleRef xlink:type="simple" xlink:href="http://www.xbrl.org/2005/xbrldt-2005.xsd#domain-member" arcroleURI="http://xbrl.org/int/dim/arcrole/domain-member" />
    <link:arcroleRef xlink:type="simple" xlink:href="http://www.xbrl.org/2005/xbrldt-2005.xsd#all" arcroleURI="http://xbrl.org/int/dim/arcrole/all" />
    <link:arcroleRef xlink:type="simple" xlink:href="http://www.xbrl.org/2005/xbrldt-2005.xsd#notAll" arcroleURI="http://xbrl.org/int/dim/arcrole/notAll" />
    <link:arcroleRef xlink:type="simple" xlink:href="http://www.xbrl.org/2005/xbrldt-2005.xsd#dimension-default" arcroleURI="http://xbrl.org/int/dim/arcrole/dimension-default" />
    <link:definitionLink xlink:type="extended" xlink:role="http://nanophase.com/role/Cover" xlink:title="00000001 - Document - Cover" />
    <link:definitionLink xlink:type="extended" xlink:role="http://nanophase.com/role/ConsolidatedBalanceSheets" xlink:title="00000002 - Statement - CONSOLIDATED BALANCE SHEETS" />
    <link:definitionLink xlink:type="extended" xlink:role="http://nanophase.com/role/ConsolidatedBalanceSheetsParenthetical" xlink:title="00000003 - Statement - CONSOLIDATED BALANCE SHEETS (Parenthetical)" />
    <link:definitionLink xlink:type="extended" xlink:role="http://nanophase.com/role/ConsolidatedStatementsOfOperations" xlink:title="00000004 - Statement - CONSOLIDATED STATEMENTS OF OPERATIONS">
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_StatementLineItems" xlink:label="loc_us-gaapStatementLineItems" />
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_StatementTable" xlink:label="loc_us-gaapStatementTable" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xbrldt:contextElement="segment" xlink:from="loc_us-gaapStatementLineItems" xlink:to="loc_us-gaapStatementTable" xlink:type="arc" order="10" xbrldt:closed="true" />
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/srt/2024/elts/srt-2024.xsd#srt_ProductOrServiceAxis" xlink:label="loc_srtProductOrServiceAxis" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaapStatementTable" xlink:to="loc_srtProductOrServiceAxis" xlink:type="arc" order="1" />
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/srt/2024/elts/srt-2024.xsd#srt_ProductsAndServicesDomain" xlink:label="loc_srtProductsAndServicesDomain" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srtProductOrServiceAxis" xlink:to="loc_srtProductsAndServicesDomain" xlink:type="arc" order="20" />
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/srt/2024/elts/srt-2024.xsd#srt_ProductsAndServicesDomain" xlink:label="loc_srtProductsAndServicesDomain_10" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xbrldt:contextElement="segment" xlink:from="loc_srtProductOrServiceAxis" xlink:to="loc_srtProductsAndServicesDomain_10" xlink:type="arc" order="30" />
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ProductMember" xlink:label="loc_us-gaapProductMember_20" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srtProductsAndServicesDomain" xlink:to="loc_us-gaapProductMember_20" xlink:type="arc" order="21" />
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ProductAndServiceOtherMember" xlink:label="loc_us-gaapProductAndServiceOtherMember_40" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srtProductsAndServicesDomain" xlink:to="loc_us-gaapProductAndServiceOtherMember_40" xlink:type="arc" order="41" />
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_RevenuesAbstract" xlink:label="loc_us-gaapRevenuesAbstract_70" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapStatementLineItems" xlink:to="loc_us-gaapRevenuesAbstract_70" xlink:type="arc" order="0" />
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_RevenueFromContractWithCustomerExcludingAssessedTax" xlink:label="loc_us-gaapRevenueFromContractWithCustomerExcludingAssessedTax_70" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapStatementLineItems" xlink:to="loc_us-gaapRevenueFromContractWithCustomerExcludingAssessedTax_70" xlink:type="arc" order="1" />
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_OperatingExpensesAbstract" xlink:label="loc_us-gaapOperatingExpensesAbstract_70" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapStatementLineItems" xlink:to="loc_us-gaapOperatingExpensesAbstract_70" xlink:type="arc" order="2" />
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_CostOfGoodsAndServicesSold" xlink:label="loc_us-gaapCostOfGoodsAndServicesSold_70" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapOperatingExpensesAbstract_70" xlink:to="loc_us-gaapCostOfGoodsAndServicesSold_70" xlink:type="arc" order="3" />
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_GrossProfit" xlink:label="loc_us-gaapGrossProfit_70" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapOperatingExpensesAbstract_70" xlink:to="loc_us-gaapGrossProfit_70" xlink:type="arc" order="4" />
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ResearchAndDevelopmentExpense" xlink:label="loc_us-gaapResearchAndDevelopmentExpense_70" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapOperatingExpensesAbstract_70" xlink:to="loc_us-gaapResearchAndDevelopmentExpense_70" xlink:type="arc" order="5" />
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_SellingGeneralAndAdministrativeExpense" xlink:label="loc_us-gaapSellingGeneralAndAdministrativeExpense_70" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapOperatingExpensesAbstract_70" xlink:to="loc_us-gaapSellingGeneralAndAdministrativeExpense_70" xlink:type="arc" order="6" />
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_OperatingIncomeLoss" xlink:label="loc_us-gaapOperatingIncomeLoss_70" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapOperatingExpensesAbstract_70" xlink:to="loc_us-gaapOperatingIncomeLoss_70" xlink:type="arc" order="7" />
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_InterestExpenseNonoperating" xlink:label="loc_us-gaapInterestExpenseNonoperating_70" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapOperatingExpensesAbstract_70" xlink:to="loc_us-gaapInterestExpenseNonoperating_70" xlink:type="arc" order="8" />
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_IncomeLossFromContinuingOperationsBeforeIncomeTaxesExtraordinaryItemsNoncontrollingInterest" xlink:label="loc_us-gaapIncomeLossFromContinuingOperationsBeforeIncomeTaxesExtraordinaryItemsNoncontrollingInterest_70" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapStatementLineItems" xlink:to="loc_us-gaapIncomeLossFromContinuingOperationsBeforeIncomeTaxesExtraordinaryItemsNoncontrollingInterest_70" xlink:type="arc" order="9" />
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_IncomeTaxExpenseBenefit" xlink:label="loc_us-gaapIncomeTaxExpenseBenefit_70" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapStatementLineItems" xlink:to="loc_us-gaapIncomeTaxExpenseBenefit_70" xlink:type="arc" order="10" />
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_NetIncomeLoss" xlink:label="loc_us-gaapNetIncomeLoss_70" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapStatementLineItems" xlink:to="loc_us-gaapNetIncomeLoss_70" xlink:type="arc" order="11" />
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_EarningsPerShareBasic" xlink:label="loc_us-gaapEarningsPerShareBasic_70" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapStatementLineItems" xlink:to="loc_us-gaapEarningsPerShareBasic_70" xlink:type="arc" order="12" />
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_WeightedAverageNumberOfSharesOutstandingBasic" xlink:label="loc_us-gaapWeightedAverageNumberOfSharesOutstandingBasic_70" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapStatementLineItems" xlink:to="loc_us-gaapWeightedAverageNumberOfSharesOutstandingBasic_70" xlink:type="arc" order="13" />
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_EarningsPerShareDiluted" xlink:label="loc_us-gaapEarningsPerShareDiluted_70" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapStatementLineItems" xlink:to="loc_us-gaapEarningsPerShareDiluted_70" xlink:type="arc" order="14" />
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_WeightedAverageNumberOfDilutedSharesOutstanding" xlink:label="loc_us-gaapWeightedAverageNumberOfDilutedSharesOutstanding_70" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapStatementLineItems" xlink:to="loc_us-gaapWeightedAverageNumberOfDilutedSharesOutstanding_70" xlink:type="arc" order="15" />
    </link:definitionLink>
    <link:definitionLink xlink:type="extended" xlink:role="http://nanophase.com/role/ConsolidatedStatementsOfStockholdersEquity" xlink:title="00000005 - Statement - CONSOLIDATED STATEMENTS OF STOCKHOLDERS&apos; EQUITY">
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_StatementLineItems" xlink:label="loc_us-gaapStatementLineItems" />
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_StatementTable" xlink:label="loc_us-gaapStatementTable" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xbrldt:contextElement="segment" xlink:from="loc_us-gaapStatementLineItems" xlink:to="loc_us-gaapStatementTable" xlink:type="arc" order="10" xbrldt:closed="true" />
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_StatementEquityComponentsAxis" xlink:label="loc_us-gaapStatementEquityComponentsAxis" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaapStatementTable" xlink:to="loc_us-gaapStatementEquityComponentsAxis" xlink:type="arc" order="1" />
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_EquityComponentDomain" xlink:label="loc_us-gaapEquityComponentDomain" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaapStatementEquityComponentsAxis" xlink:to="loc_us-gaapEquityComponentDomain" xlink:type="arc" order="20" />
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_EquityComponentDomain" xlink:label="loc_us-gaapEquityComponentDomain_10" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xbrldt:contextElement="segment" xlink:from="loc_us-gaapStatementEquityComponentsAxis" xlink:to="loc_us-gaapEquityComponentDomain_10" xlink:type="arc" order="30" />
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_PreferredStockMember" xlink:label="loc_us-gaapPreferredStockMember_0" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapEquityComponentDomain" xlink:to="loc_us-gaapPreferredStockMember_0" xlink:type="arc" order="1" />
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_CommonStockMember" xlink:label="loc_us-gaapCommonStockMember_10" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapEquityComponentDomain" xlink:to="loc_us-gaapCommonStockMember_10" xlink:type="arc" order="11" />
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_AdditionalPaidInCapitalMember" xlink:label="loc_us-gaapAdditionalPaidInCapitalMember_20" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapEquityComponentDomain" xlink:to="loc_us-gaapAdditionalPaidInCapitalMember_20" xlink:type="arc" order="21" />
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_RetainedEarningsMember" xlink:label="loc_us-gaapRetainedEarningsMember_30" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapEquityComponentDomain" xlink:to="loc_us-gaapRetainedEarningsMember_30" xlink:type="arc" order="31" />
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_StockholdersEquity" xlink:label="loc_us-gaapStockholdersEquity_60" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapStatementLineItems" xlink:to="loc_us-gaapStockholdersEquity_60" xlink:type="arc" order="1" />
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_SharesOutstanding" xlink:label="loc_us-gaapSharesOutstanding_60" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapStatementLineItems" xlink:to="loc_us-gaapSharesOutstanding_60" xlink:type="arc" order="2" />
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_StockholdersEquityOther" xlink:label="loc_us-gaapStockholdersEquityOther_60" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapStatementLineItems" xlink:to="loc_us-gaapStockholdersEquityOther_60" xlink:type="arc" order="3" />
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_StockIssuedDuringPeriodValueNewIssues" xlink:label="loc_us-gaapStockIssuedDuringPeriodValueNewIssues_60" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapStatementLineItems" xlink:to="loc_us-gaapStockIssuedDuringPeriodValueNewIssues_60" xlink:type="arc" order="4" />
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_StockIssuedDuringPeriodSharesNewIssues" xlink:label="loc_us-gaapStockIssuedDuringPeriodSharesNewIssues_60" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapStatementLineItems" xlink:to="loc_us-gaapStockIssuedDuringPeriodSharesNewIssues_60" xlink:type="arc" order="5" />
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_AdjustmentsToAdditionalPaidInCapitalSharebasedCompensationRequisiteServicePeriodRecognitionValue" xlink:label="loc_us-gaapAdjustmentsToAdditionalPaidInCapitalSharebasedCompensationRequisiteServicePeriodRecognitionValue_60" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapStatementLineItems" xlink:to="loc_us-gaapAdjustmentsToAdditionalPaidInCapitalSharebasedCompensationRequisiteServicePeriodRecognitionValue_60" xlink:type="arc" order="6" />
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_AdjustmentsToAdditionalPaidInCapitalStockIssuedIssuanceCosts" xlink:label="loc_us-gaapAdjustmentsToAdditionalPaidInCapitalStockIssuedIssuanceCosts_60" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapStatementLineItems" xlink:to="loc_us-gaapAdjustmentsToAdditionalPaidInCapitalStockIssuedIssuanceCosts_60" xlink:type="arc" order="7" />
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_NetIncomeLoss" xlink:label="loc_us-gaapNetIncomeLoss_60" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapStatementLineItems" xlink:to="loc_us-gaapNetIncomeLoss_60" xlink:type="arc" order="8" />
    </link:definitionLink>
    <link:definitionLink xlink:type="extended" xlink:role="http://nanophase.com/role/ConsolidatedStatementsOfCashFlows" xlink:title="00000006 - Statement - CONSOLIDATED STATEMENTS OF CASH FLOWS" />
    <link:definitionLink xlink:type="extended" xlink:role="http://xbrl.sec.gov/cyd/role/CybersecurityRiskManagementAndStrategyDisclosure" xlink:title="00000012 - Disclosure - Cybersecurity Risk Management and Strategy Disclosure" />
    <link:definitionLink xlink:type="extended" xlink:role="http://xbrl.sec.gov/cyd/role/MaterialCybersecurityIncidentDisclosure" xlink:title="00000013 - Disclosure - Material Cybersecurity Incident Disclosure" />
    <link:definitionLink xlink:type="extended" xlink:role="http://nanophase.com/role/RiskAssessmentAndStrategy" xlink:title="999014 - Disclosure - Risk Assessment and Strategy" />
    <link:definitionLink xlink:type="extended" xlink:role="http://nanophase.com/role/ManagementOversight" xlink:title="999015 - Disclosure - Management Oversight" />
    <link:definitionLink xlink:type="extended" xlink:role="http://nanophase.com/role/DescriptionOfBusiness" xlink:title="999016 - Disclosure - Description of Business" />
    <link:definitionLink xlink:type="extended" xlink:role="http://nanophase.com/role/SummaryOfSignificantAccountingPolicies" xlink:title="999017 - Disclosure - Summary of Significant Accounting Policies" />
    <link:definitionLink xlink:type="extended" xlink:role="http://nanophase.com/role/RelatedPartyNotesAndLinesOfCredit" xlink:title="999018 - Disclosure - Related Party Notes and Lines of Credit" />
    <link:definitionLink xlink:type="extended" xlink:role="http://nanophase.com/role/InventoriesNet" xlink:title="999019 - Disclosure - Inventories, net" />
    <link:definitionLink xlink:type="extended" xlink:role="http://nanophase.com/role/EquipmentAndLeaseholdImprovements" xlink:title="999020 - Disclosure - Equipment and Leasehold Improvements" />
    <link:definitionLink xlink:type="extended" xlink:role="http://nanophase.com/role/LeaseCommitments" xlink:title="999021 - Disclosure - Lease Commitments" />
    <link:definitionLink xlink:type="extended" xlink:role="http://nanophase.com/role/AccruedExpenses" xlink:title="999022 - Disclosure - Accrued Expenses" />
    <link:definitionLink xlink:type="extended" xlink:role="http://nanophase.com/role/IncomeTaxes" xlink:title="999023 - Disclosure - Income Taxes" />
    <link:definitionLink xlink:type="extended" xlink:role="http://nanophase.com/role/CapitalStock" xlink:title="999024 - Disclosure - Capital Stock" />
    <link:definitionLink xlink:type="extended" xlink:role="http://nanophase.com/role/StockOptionsAndStockGrants" xlink:title="999025 - Disclosure - Stock Options and Stock Grants" />
    <link:definitionLink xlink:type="extended" xlink:role="http://nanophase.com/role/KProfit-sharingPlan" xlink:title="999026 - Disclosure - 401(k) Profit-Sharing Plan" />
    <link:definitionLink xlink:type="extended" xlink:role="http://nanophase.com/role/SignificantCustomers" xlink:title="999027 - Disclosure - Significant Customers" />
    <link:definitionLink xlink:type="extended" xlink:role="http://nanophase.com/role/BusinessSegmentationAndGeographicalDistribution" xlink:title="999028 - Disclosure - Business Segmentation and Geographical Distribution" />
    <link:definitionLink xlink:type="extended" xlink:role="http://nanophase.com/role/SubsequentEvent" xlink:title="999029 - Disclosure - Subsequent Event" />
    <link:definitionLink xlink:type="extended" xlink:role="http://nanophase.com/role/SummaryOfSignificantAccountingPoliciesPolicies" xlink:title="999030 - Disclosure - Summary of Significant Accounting Policies (Policies)" />
    <link:definitionLink xlink:type="extended" xlink:role="http://nanophase.com/role/SummaryOfSignificantAccountingPoliciesTables" xlink:title="999031 - Disclosure - Summary of Significant Accounting Policies (Tables)" />
    <link:definitionLink xlink:type="extended" xlink:role="http://nanophase.com/role/RelatedPartyNotesAndLinesOfCreditTables" xlink:title="999032 - Disclosure - Related Party Notes and Lines of Credit (Tables)" />
    <link:definitionLink xlink:type="extended" xlink:role="http://nanophase.com/role/InventoriesNetTables" xlink:title="999033 - Disclosure - Inventories, net (Tables)" />
    <link:definitionLink xlink:type="extended" xlink:role="http://nanophase.com/role/EquipmentAndLeaseholdImprovementsTables" xlink:title="999034 - Disclosure - Equipment and Leasehold Improvements (Tables)" />
    <link:definitionLink xlink:type="extended" xlink:role="http://nanophase.com/role/LeaseCommitmentsTables" xlink:title="999035 - Disclosure - Lease Commitments (Tables)" />
    <link:definitionLink xlink:type="extended" xlink:role="http://nanophase.com/role/AccruedExpensesTables" xlink:title="999036 - Disclosure - Accrued Expenses (Tables)" />
    <link:definitionLink xlink:type="extended" xlink:role="http://nanophase.com/role/IncomeTaxesTables" xlink:title="999037 - Disclosure - Income Taxes (Tables)" />
    <link:definitionLink xlink:type="extended" xlink:role="http://nanophase.com/role/StockOptionsAndStockGrantsTables" xlink:title="999038 - Disclosure - Stock Options and Stock Grants (Tables)" />
    <link:definitionLink xlink:type="extended" xlink:role="http://nanophase.com/role/SignificantCustomersTables" xlink:title="999039 - Disclosure - Significant Customers (Tables)" />
    <link:definitionLink xlink:type="extended" xlink:role="http://nanophase.com/role/BusinessSegmentationAndGeographicalDistributionTables" xlink:title="999040 - Disclosure - Business Segmentation and Geographical Distribution (Tables)" />
    <link:definitionLink xlink:type="extended" xlink:role="http://nanophase.com/role/WeDetermineAllowanceForCreditLossesByIdentifyingTroubledAccountsAndByUsingHistoricalExperienceAppliedToAgingOfAccountsAsWellAsExpectedLossesBasedOnCurrentAndAnticipatedMacroeconomicEnvironment.Details" xlink:title="999041 - Disclosure - We determine the allowance for credit losses by identifying troubled accounts and by using historical experience applied to an aging of accounts, as well as expected losses based on the current and anticipated macroeconomic environment. (Details)" />
    <link:definitionLink xlink:type="extended" xlink:role="http://nanophase.com/role/ContractBalancesForYearsEndedDecember3120242023And2022AreAsFollowsDetails" xlink:title="999042 - Disclosure - Contract balances for the years ended December 31, 2024, 2023, and 2022 are as follows: (Details)" />
    <link:definitionLink xlink:type="extended" xlink:role="http://nanophase.com/role/EarningsApplicableToCommonStockAndCommonStockSharesUsedInCalculationOfBasicAndDilutedEarningsPerShareAreAsFollowsDetails" xlink:title="999043 - Disclosure - Earnings applicable to common stock and common stock shares used in the calculation of basic and diluted earnings per share are as follows (Details)" />
    <link:definitionLink xlink:type="extended" xlink:role="http://nanophase.com/role/SummaryOfSignificantAccountingPoliciesDetailsNarrative" xlink:title="999044 - Disclosure - Summary of Significant Accounting Policies (Details Narrative)">
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_PropertyPlantAndEquipmentLineItems" xlink:label="loc_us-gaapPropertyPlantAndEquipmentLineItems" />
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ScheduleOfPropertyPlantAndEquipmentTable" xlink:label="loc_us-gaapScheduleOfPropertyPlantAndEquipmentTable" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xbrldt:contextElement="segment" xlink:from="loc_us-gaapPropertyPlantAndEquipmentLineItems" xlink:to="loc_us-gaapScheduleOfPropertyPlantAndEquipmentTable" xlink:type="arc" order="10" xbrldt:closed="true" />
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_PropertyPlantAndEquipmentByTypeAxis" xlink:label="loc_us-gaapPropertyPlantAndEquipmentByTypeAxis" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaapScheduleOfPropertyPlantAndEquipmentTable" xlink:to="loc_us-gaapPropertyPlantAndEquipmentByTypeAxis" xlink:type="arc" order="1" />
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_PropertyPlantAndEquipmentTypeDomain" xlink:label="loc_us-gaapPropertyPlantAndEquipmentTypeDomain" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaapPropertyPlantAndEquipmentByTypeAxis" xlink:to="loc_us-gaapPropertyPlantAndEquipmentTypeDomain" xlink:type="arc" order="20" />
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_PropertyPlantAndEquipmentTypeDomain" xlink:label="loc_us-gaapPropertyPlantAndEquipmentTypeDomain_10" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xbrldt:contextElement="segment" xlink:from="loc_us-gaapPropertyPlantAndEquipmentByTypeAxis" xlink:to="loc_us-gaapPropertyPlantAndEquipmentTypeDomain_10" xlink:type="arc" order="30" />
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_EquipmentMember" xlink:label="loc_us-gaapEquipmentMember_0" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapPropertyPlantAndEquipmentTypeDomain" xlink:to="loc_us-gaapEquipmentMember_0" xlink:type="arc" order="1" />
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_LeaseholdImprovementsMember" xlink:label="loc_us-gaapLeaseholdImprovementsMember_20" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapPropertyPlantAndEquipmentTypeDomain" xlink:to="loc_us-gaapLeaseholdImprovementsMember_20" xlink:type="arc" order="21" />
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_OtherCapitalizedPropertyPlantAndEquipmentMember" xlink:label="loc_us-gaapOtherCapitalizedPropertyPlantAndEquipmentMember_40" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapPropertyPlantAndEquipmentTypeDomain" xlink:to="loc_us-gaapOtherCapitalizedPropertyPlantAndEquipmentMember_40" xlink:type="arc" order="41" />
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/srt/2024/elts/srt-2024.xsd#srt_RangeAxis" xlink:label="loc_srtRangeAxis" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaapScheduleOfPropertyPlantAndEquipmentTable" xlink:to="loc_srtRangeAxis" xlink:type="arc" order="2" />
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/srt/2024/elts/srt-2024.xsd#srt_RangeMember" xlink:label="loc_srtRangeMember" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srtRangeAxis" xlink:to="loc_srtRangeMember" xlink:type="arc" order="20" />
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/srt/2024/elts/srt-2024.xsd#srt_RangeMember" xlink:label="loc_srtRangeMember_10" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xbrldt:contextElement="segment" xlink:from="loc_srtRangeAxis" xlink:to="loc_srtRangeMember_10" xlink:type="arc" order="30" />
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/srt/2024/elts/srt-2024.xsd#srt_MinimumMember" xlink:label="loc_srtMinimumMember_0" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srtRangeMember" xlink:to="loc_srtMinimumMember_0" xlink:type="arc" order="2" />
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/srt/2024/elts/srt-2024.xsd#srt_MaximumMember" xlink:label="loc_srtMaximumMember_10" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srtRangeMember" xlink:to="loc_srtMaximumMember_10" xlink:type="arc" order="12" />
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_RelatedPartyTransactionAxis" xlink:label="loc_us-gaapRelatedPartyTransactionAxis" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaapScheduleOfPropertyPlantAndEquipmentTable" xlink:to="loc_us-gaapRelatedPartyTransactionAxis" xlink:type="arc" order="3" />
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_RelatedPartyTransactionDomain" xlink:label="loc_us-gaapRelatedPartyTransactionDomain" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaapRelatedPartyTransactionAxis" xlink:to="loc_us-gaapRelatedPartyTransactionDomain" xlink:type="arc" order="20" />
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_RelatedPartyTransactionDomain" xlink:label="loc_us-gaapRelatedPartyTransactionDomain_10" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xbrldt:contextElement="segment" xlink:from="loc_us-gaapRelatedPartyTransactionAxis" xlink:to="loc_us-gaapRelatedPartyTransactionDomain_10" xlink:type="arc" order="30" />
      <link:loc xlink:type="locator" xlink:href="nanx-20241231.xsd#nanx_PrepaymentsFromCertainCustomersPerCompanyPolicyMember" xlink:label="loc_nanxPrepaymentsFromCertainCustomersPerCompanyPolicyMember_70" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapRelatedPartyTransactionDomain" xlink:to="loc_nanxPrepaymentsFromCertainCustomersPerCompanyPolicyMember_70" xlink:type="arc" order="71" />
      <link:loc xlink:type="locator" xlink:href="nanx-20241231.xsd#nanx_PrepaymentsFromProductDevelopmentAgreementWithAPersonalCareIngredientCustomerMember" xlink:label="loc_nanxPrepaymentsFromProductDevelopmentAgreementWithAPersonalCareIngredientCustomerMember_80" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapRelatedPartyTransactionDomain" xlink:to="loc_nanxPrepaymentsFromProductDevelopmentAgreementWithAPersonalCareIngredientCustomerMember_80" xlink:type="arc" order="81" />
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_TimingOfTransferOfGoodOrServiceAxis" xlink:label="loc_us-gaapTimingOfTransferOfGoodOrServiceAxis" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaapScheduleOfPropertyPlantAndEquipmentTable" xlink:to="loc_us-gaapTimingOfTransferOfGoodOrServiceAxis" xlink:type="arc" order="4" />
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_TimingOfTransferOfGoodOrServiceDomain" xlink:label="loc_us-gaapTimingOfTransferOfGoodOrServiceDomain" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaapTimingOfTransferOfGoodOrServiceAxis" xlink:to="loc_us-gaapTimingOfTransferOfGoodOrServiceDomain" xlink:type="arc" order="20" />
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_TimingOfTransferOfGoodOrServiceDomain" xlink:label="loc_us-gaapTimingOfTransferOfGoodOrServiceDomain_10" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xbrldt:contextElement="segment" xlink:from="loc_us-gaapTimingOfTransferOfGoodOrServiceAxis" xlink:to="loc_us-gaapTimingOfTransferOfGoodOrServiceDomain_10" xlink:type="arc" order="30" />
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_TransferredOverTimeMember" xlink:label="loc_us-gaapTransferredOverTimeMember_110" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapTimingOfTransferOfGoodOrServiceDomain" xlink:to="loc_us-gaapTransferredOverTimeMember_110" xlink:type="arc" order="111" />
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_PropertyPlantAndEquipmentUsefulLife" xlink:label="loc_us-gaapPropertyPlantAndEquipmentUsefulLife_140" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapPropertyPlantAndEquipmentLineItems" xlink:to="loc_us-gaapPropertyPlantAndEquipmentUsefulLife_140" xlink:type="arc" order="0" />
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_DeferredIncome" xlink:label="loc_us-gaapDeferredIncome_140" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapPropertyPlantAndEquipmentLineItems" xlink:to="loc_us-gaapDeferredIncome_140" xlink:type="arc" order="1" />
      <link:loc xlink:type="locator" xlink:href="nanx-20241231.xsd#nanx_PercentageOfPrepayments" xlink:label="loc_nanxPercentageOfPrepayments_140" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapPropertyPlantAndEquipmentLineItems" xlink:to="loc_nanxPercentageOfPrepayments_140" xlink:type="arc" order="2" />
      <link:loc xlink:type="locator" xlink:href="nanx-20241231.xsd#nanx_VolumeRebates" xlink:label="loc_nanxVolumeRebates_140" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapPropertyPlantAndEquipmentLineItems" xlink:to="loc_nanxVolumeRebates_140" xlink:type="arc" order="3" />
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ContractWithCustomerLiabilityRevenueRecognized" xlink:label="loc_us-gaapContractWithCustomerLiabilityRevenueRecognized_140" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapPropertyPlantAndEquipmentLineItems" xlink:to="loc_us-gaapContractWithCustomerLiabilityRevenueRecognized_140" xlink:type="arc" order="4" />
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_RevenueFromContractWithCustomerExcludingAssessedTax" xlink:label="loc_us-gaapRevenueFromContractWithCustomerExcludingAssessedTax_140" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapPropertyPlantAndEquipmentLineItems" xlink:to="loc_us-gaapRevenueFromContractWithCustomerExcludingAssessedTax_140" xlink:type="arc" order="5" />
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_WeightedAverageNumberDilutedSharesOutstandingAdjustment" xlink:label="loc_us-gaapWeightedAverageNumberDilutedSharesOutstandingAdjustment_140" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapPropertyPlantAndEquipmentLineItems" xlink:to="loc_us-gaapWeightedAverageNumberDilutedSharesOutstandingAdjustment_140" xlink:type="arc" order="6" />
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareAmount" xlink:label="loc_us-gaapAntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareAmount_140" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapPropertyPlantAndEquipmentLineItems" xlink:to="loc_us-gaapAntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareAmount_140" xlink:type="arc" order="7" />
    </link:definitionLink>
    <link:definitionLink xlink:type="extended" xlink:role="http://nanophase.com/role/NotesAndLinesOfCreditConsistOfFollowingDetails" xlink:title="999045 - Disclosure - Notes and lines of credit consist of the following (Details)">
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_LineOfCreditFacilityLineItems" xlink:label="loc_us-gaapLineOfCreditFacilityLineItems" />
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_LineOfCreditFacilityTable" xlink:label="loc_us-gaapLineOfCreditFacilityTable" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xbrldt:contextElement="segment" xlink:from="loc_us-gaapLineOfCreditFacilityLineItems" xlink:to="loc_us-gaapLineOfCreditFacilityTable" xlink:type="arc" order="10" xbrldt:closed="true" />
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_CreditFacilityAxis" xlink:label="loc_us-gaapCreditFacilityAxis" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaapLineOfCreditFacilityTable" xlink:to="loc_us-gaapCreditFacilityAxis" xlink:type="arc" order="1" />
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_CreditFacilityDomain" xlink:label="loc_us-gaapCreditFacilityDomain" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaapCreditFacilityAxis" xlink:to="loc_us-gaapCreditFacilityDomain" xlink:type="arc" order="20" />
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_CreditFacilityDomain" xlink:label="loc_us-gaapCreditFacilityDomain_10" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xbrldt:contextElement="segment" xlink:from="loc_us-gaapCreditFacilityAxis" xlink:to="loc_us-gaapCreditFacilityDomain_10" xlink:type="arc" order="30" />
      <link:loc xlink:type="locator" xlink:href="nanx-20241231.xsd#nanx_LibertyvilleBankAndTrustMember" xlink:label="loc_nanxLibertyvilleBankAndTrustMember_0" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapCreditFacilityDomain" xlink:to="loc_nanxLibertyvilleBankAndTrustMember_0" xlink:type="arc" order="1" />
      <link:loc xlink:type="locator" xlink:href="nanx-20241231.xsd#nanx_LibertyvilleBankAndTrustOneMember" xlink:label="loc_nanxLibertyvilleBankAndTrustOneMember_30" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapCreditFacilityDomain" xlink:to="loc_nanxLibertyvilleBankAndTrustOneMember_30" xlink:type="arc" order="31" />
      <link:loc xlink:type="locator" xlink:href="nanx-20241231.xsd#nanx_BeachcorpLLCMember" xlink:label="loc_nanxBeachcorpLLCMember_60" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapCreditFacilityDomain" xlink:to="loc_nanxBeachcorpLLCMember_60" xlink:type="arc" order="61" />
      <link:loc xlink:type="locator" xlink:href="nanx-20241231.xsd#nanx_BeachcorpLLCOneMember" xlink:label="loc_nanxBeachcorpLLCOneMember_90" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapCreditFacilityDomain" xlink:to="loc_nanxBeachcorpLLCOneMember_90" xlink:type="arc" order="91" />
      <link:loc xlink:type="locator" xlink:href="nanx-20241231.xsd#nanx_StrandlerLLCMember" xlink:label="loc_nanxStrandlerLLCMember_130" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapCreditFacilityDomain" xlink:to="loc_nanxStrandlerLLCMember_130" xlink:type="arc" order="131" />
      <link:loc xlink:type="locator" xlink:href="nanx-20241231.xsd#nanx_StrandlerLLCOneMember" xlink:label="loc_nanxStrandlerLLCOneMember_160" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapCreditFacilityDomain" xlink:to="loc_nanxStrandlerLLCOneMember_160" xlink:type="arc" order="161" />
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_LetterOfCreditMember" xlink:label="loc_us-gaapLetterOfCreditMember_190" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapCreditFacilityDomain" xlink:to="loc_us-gaapLetterOfCreditMember_190" xlink:type="arc" order="191" />
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_RevolvingCreditFacilityMember" xlink:label="loc_us-gaapRevolvingCreditFacilityMember_220" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapCreditFacilityDomain" xlink:to="loc_us-gaapRevolvingCreditFacilityMember_220" xlink:type="arc" order="222" />
      <link:loc xlink:type="locator" xlink:href="nanx-20241231.xsd#nanx_InventoryFacilityMember" xlink:label="loc_nanxInventoryFacilityMember_260" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapCreditFacilityDomain" xlink:to="loc_nanxInventoryFacilityMember_260" xlink:type="arc" order="262" />
      <link:loc xlink:type="locator" xlink:href="nanx-20241231.xsd#nanx_ReplacementPromissoryNoteMember" xlink:label="loc_nanxReplacementPromissoryNoteMember_280" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapCreditFacilityDomain" xlink:to="loc_nanxReplacementPromissoryNoteMember_280" xlink:type="arc" order="282" />
      <link:loc xlink:type="locator" xlink:href="nanx-20241231.xsd#nanx_TermLoanMember" xlink:label="loc_nanxTermLoanMember_320" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapCreditFacilityDomain" xlink:to="loc_nanxTermLoanMember_320" xlink:type="arc" order="321" />
      <link:loc xlink:type="locator" xlink:href="nanx-20241231.xsd#nanx_BridgeNoteMember" xlink:label="loc_nanxBridgeNoteMember_340" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapCreditFacilityDomain" xlink:to="loc_nanxBridgeNoteMember_340" xlink:type="arc" order="341" />
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ShortTermDebtTypeAxis" xlink:label="loc_us-gaapShortTermDebtTypeAxis" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaapLineOfCreditFacilityTable" xlink:to="loc_us-gaapShortTermDebtTypeAxis" xlink:type="arc" order="2" />
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ShortTermDebtTypeDomain" xlink:label="loc_us-gaapShortTermDebtTypeDomain" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaapShortTermDebtTypeAxis" xlink:to="loc_us-gaapShortTermDebtTypeDomain" xlink:type="arc" order="20" />
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ShortTermDebtTypeDomain" xlink:label="loc_us-gaapShortTermDebtTypeDomain_10" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xbrldt:contextElement="segment" xlink:from="loc_us-gaapShortTermDebtTypeAxis" xlink:to="loc_us-gaapShortTermDebtTypeDomain_10" xlink:type="arc" order="30" />
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_LetterOfCreditMember" xlink:label="loc_us-gaapLetterOfCreditMember_200" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapShortTermDebtTypeDomain" xlink:to="loc_us-gaapLetterOfCreditMember_200" xlink:type="arc" order="201" />
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_TypeOfArrangementAxis" xlink:label="loc_us-gaapTypeOfArrangementAxis" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaapLineOfCreditFacilityTable" xlink:to="loc_us-gaapTypeOfArrangementAxis" xlink:type="arc" order="3" />
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ArrangementsAndNonarrangementTransactionsMember" xlink:label="loc_us-gaapArrangementsAndNonarrangementTransactionsMember" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaapTypeOfArrangementAxis" xlink:to="loc_us-gaapArrangementsAndNonarrangementTransactionsMember" xlink:type="arc" order="20" />
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ArrangementsAndNonarrangementTransactionsMember" xlink:label="loc_us-gaapArrangementsAndNonarrangementTransactionsMember_10" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xbrldt:contextElement="segment" xlink:from="loc_us-gaapTypeOfArrangementAxis" xlink:to="loc_us-gaapArrangementsAndNonarrangementTransactionsMember_10" xlink:type="arc" order="30" />
      <link:loc xlink:type="locator" xlink:href="nanx-20241231.xsd#nanx_BusinessLoanAgreementMember" xlink:label="loc_nanxBusinessLoanAgreementMember_220" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapArrangementsAndNonarrangementTransactionsMember" xlink:to="loc_nanxBusinessLoanAgreementMember_220" xlink:type="arc" order="221" />
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/srt/2024/elts/srt-2024.xsd#srt_CounterpartyNameAxis" xlink:label="loc_srtCounterpartyNameAxis" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaapLineOfCreditFacilityTable" xlink:to="loc_srtCounterpartyNameAxis" xlink:type="arc" order="4" />
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/srt/2024/elts/srt-2024.xsd#srt_RepurchaseAgreementCounterpartyNameDomain" xlink:label="loc_srtRepurchaseAgreementCounterpartyNameDomain" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srtCounterpartyNameAxis" xlink:to="loc_srtRepurchaseAgreementCounterpartyNameDomain" xlink:type="arc" order="20" />
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/srt/2024/elts/srt-2024.xsd#srt_RepurchaseAgreementCounterpartyNameDomain" xlink:label="loc_srtRepurchaseAgreementCounterpartyNameDomain_10" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xbrldt:contextElement="segment" xlink:from="loc_srtCounterpartyNameAxis" xlink:to="loc_srtRepurchaseAgreementCounterpartyNameDomain_10" xlink:type="arc" order="30" />
      <link:loc xlink:type="locator" xlink:href="nanx-20241231.xsd#nanx_BeachcorpLLCMember" xlink:label="loc_nanxBeachcorpLLCMember_220" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srtRepurchaseAgreementCounterpartyNameDomain" xlink:to="loc_nanxBeachcorpLLCMember_220" xlink:type="arc" order="223" />
      <link:loc xlink:type="locator" xlink:href="nanx-20241231.xsd#nanx_StrandlerLLCMember" xlink:label="loc_nanxStrandlerLLCMember_320" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srtRepurchaseAgreementCounterpartyNameDomain" xlink:to="loc_nanxStrandlerLLCMember_320" xlink:type="arc" order="322" />
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_RelatedPartyTransactionRate" xlink:label="loc_us-gaapRelatedPartyTransactionRate_370" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapLineOfCreditFacilityLineItems" xlink:to="loc_us-gaapRelatedPartyTransactionRate_370" xlink:type="arc" order="0" />
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_LineOfCreditFacilityCurrentBorrowingCapacity" xlink:label="loc_us-gaapLineOfCreditFacilityCurrentBorrowingCapacity_370" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapLineOfCreditFacilityLineItems" xlink:to="loc_us-gaapLineOfCreditFacilityCurrentBorrowingCapacity_370" xlink:type="arc" order="1" />
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_LineOfCredit" xlink:label="loc_us-gaapLineOfCredit_370" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapLineOfCreditFacilityLineItems" xlink:to="loc_us-gaapLineOfCredit_370" xlink:type="arc" order="2" />
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_LineOfCreditFacilityMaximumBorrowingCapacity" xlink:label="loc_us-gaapLineOfCreditFacilityMaximumBorrowingCapacity_370" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapLineOfCreditFacilityLineItems" xlink:to="loc_us-gaapLineOfCreditFacilityMaximumBorrowingCapacity_370" xlink:type="arc" order="3" />
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_DebtInstrumentDescriptionOfVariableRateBasis" xlink:label="loc_us-gaapDebtInstrumentDescriptionOfVariableRateBasis_370" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapLineOfCreditFacilityLineItems" xlink:to="loc_us-gaapDebtInstrumentDescriptionOfVariableRateBasis_370" xlink:type="arc" order="4" />
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_DebtInstrumentBasisSpreadOnVariableRate1" xlink:label="loc_us-gaapDebtInstrumentBasisSpreadOnVariableRate1_370" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapLineOfCreditFacilityLineItems" xlink:to="loc_us-gaapDebtInstrumentBasisSpreadOnVariableRate1_370" xlink:type="arc" order="5" />
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_LineOfCreditFacilityExpirationDate1" xlink:label="loc_us-gaapLineOfCreditFacilityExpirationDate1_370" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapLineOfCreditFacilityLineItems" xlink:to="loc_us-gaapLineOfCreditFacilityExpirationDate1_370" xlink:type="arc" order="6" />
      <link:loc xlink:type="locator" xlink:href="nanx-20241231.xsd#nanx_LineOfCreditPercentageOfEligibleInventory" xlink:label="loc_nanxLineOfCreditPercentageOfEligibleInventory_370" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapLineOfCreditFacilityLineItems" xlink:to="loc_nanxLineOfCreditPercentageOfEligibleInventory_370" xlink:type="arc" order="7" />
    </link:definitionLink>
    <link:definitionLink xlink:type="extended" xlink:role="http://nanophase.com/role/RelatedPartyInterestExpenseConsistsOfFollowingDetails" xlink:title="999046 - Disclosure - Related party interest expense consists of the following (Details)">
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_LineOfCreditFacilityLineItems" xlink:label="loc_us-gaapLineOfCreditFacilityLineItems" />
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_LineOfCreditFacilityTable" xlink:label="loc_us-gaapLineOfCreditFacilityTable" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xbrldt:contextElement="segment" xlink:from="loc_us-gaapLineOfCreditFacilityLineItems" xlink:to="loc_us-gaapLineOfCreditFacilityTable" xlink:type="arc" order="10" xbrldt:closed="true" />
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_RelatedPartyTransactionsByRelatedPartyAxis" xlink:label="loc_us-gaapRelatedPartyTransactionsByRelatedPartyAxis" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaapLineOfCreditFacilityTable" xlink:to="loc_us-gaapRelatedPartyTransactionsByRelatedPartyAxis" xlink:type="arc" order="1" />
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_RelatedPartyDomain" xlink:label="loc_us-gaapRelatedPartyDomain" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaapRelatedPartyTransactionsByRelatedPartyAxis" xlink:to="loc_us-gaapRelatedPartyDomain" xlink:type="arc" order="20" />
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_RelatedPartyDomain" xlink:label="loc_us-gaapRelatedPartyDomain_10" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xbrldt:contextElement="segment" xlink:from="loc_us-gaapRelatedPartyTransactionsByRelatedPartyAxis" xlink:to="loc_us-gaapRelatedPartyDomain_10" xlink:type="arc" order="30" />
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_RelatedPartyMember" xlink:label="loc_us-gaapRelatedPartyMember_0" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapRelatedPartyDomain" xlink:to="loc_us-gaapRelatedPartyMember_0" xlink:type="arc" order="1" />
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_CreditFacilityAxis" xlink:label="loc_us-gaapCreditFacilityAxis" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaapLineOfCreditFacilityTable" xlink:to="loc_us-gaapCreditFacilityAxis" xlink:type="arc" order="2" />
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_CreditFacilityDomain" xlink:label="loc_us-gaapCreditFacilityDomain" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaapCreditFacilityAxis" xlink:to="loc_us-gaapCreditFacilityDomain" xlink:type="arc" order="20" />
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_CreditFacilityDomain" xlink:label="loc_us-gaapCreditFacilityDomain_10" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xbrldt:contextElement="segment" xlink:from="loc_us-gaapCreditFacilityAxis" xlink:to="loc_us-gaapCreditFacilityDomain_10" xlink:type="arc" order="30" />
      <link:loc xlink:type="locator" xlink:href="nanx-20241231.xsd#nanx_BeachcorpLLCMember" xlink:label="loc_nanxBeachcorpLLCMember_40" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapCreditFacilityDomain" xlink:to="loc_nanxBeachcorpLLCMember_40" xlink:type="arc" order="41" />
      <link:loc xlink:type="locator" xlink:href="nanx-20241231.xsd#nanx_StrandlerLLCMember" xlink:label="loc_nanxStrandlerLLCMember_60" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapCreditFacilityDomain" xlink:to="loc_nanxStrandlerLLCMember_60" xlink:type="arc" order="61" />
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_InterestExpense" xlink:label="loc_us-gaapInterestExpense_90" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapLineOfCreditFacilityLineItems" xlink:to="loc_us-gaapInterestExpense_90" xlink:type="arc" order="0" />
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_InterestPayableCurrentAndNoncurrent" xlink:label="loc_us-gaapInterestPayableCurrentAndNoncurrent_90" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapLineOfCreditFacilityLineItems" xlink:to="loc_us-gaapInterestPayableCurrentAndNoncurrent_90" xlink:type="arc" order="1" />
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_RelatedPartyTransactionAmountsOfTransaction" xlink:label="loc_us-gaapRelatedPartyTransactionAmountsOfTransaction_90" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapLineOfCreditFacilityLineItems" xlink:to="loc_us-gaapRelatedPartyTransactionAmountsOfTransaction_90" xlink:type="arc" order="2" />
    </link:definitionLink>
    <link:definitionLink xlink:type="extended" xlink:role="http://nanophase.com/role/InventoriesConsistOfFollowingDetails" xlink:title="999047 - Disclosure - Inventories consist of the following (Details)" />
    <link:definitionLink xlink:type="extended" xlink:role="http://nanophase.com/role/EquipmentAndLeaseholdImprovementsConsistOfFollowingDetails" xlink:title="999048 - Disclosure - Equipment and leasehold improvements consist of the following (Details)">
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_PropertyPlantAndEquipmentLineItems" xlink:label="loc_us-gaapPropertyPlantAndEquipmentLineItems" />
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ScheduleOfPropertyPlantAndEquipmentTable" xlink:label="loc_us-gaapScheduleOfPropertyPlantAndEquipmentTable" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xbrldt:contextElement="segment" xlink:from="loc_us-gaapPropertyPlantAndEquipmentLineItems" xlink:to="loc_us-gaapScheduleOfPropertyPlantAndEquipmentTable" xlink:type="arc" order="10" xbrldt:closed="true" />
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_PropertyPlantAndEquipmentByTypeAxis" xlink:label="loc_us-gaapPropertyPlantAndEquipmentByTypeAxis" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaapScheduleOfPropertyPlantAndEquipmentTable" xlink:to="loc_us-gaapPropertyPlantAndEquipmentByTypeAxis" xlink:type="arc" order="1" />
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_PropertyPlantAndEquipmentTypeDomain" xlink:label="loc_us-gaapPropertyPlantAndEquipmentTypeDomain" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaapPropertyPlantAndEquipmentByTypeAxis" xlink:to="loc_us-gaapPropertyPlantAndEquipmentTypeDomain" xlink:type="arc" order="20" />
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_PropertyPlantAndEquipmentTypeDomain" xlink:label="loc_us-gaapPropertyPlantAndEquipmentTypeDomain_10" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xbrldt:contextElement="segment" xlink:from="loc_us-gaapPropertyPlantAndEquipmentByTypeAxis" xlink:to="loc_us-gaapPropertyPlantAndEquipmentTypeDomain_10" xlink:type="arc" order="30" />
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_MachineryAndEquipmentMember" xlink:label="loc_us-gaapMachineryAndEquipmentMember_0" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapPropertyPlantAndEquipmentTypeDomain" xlink:to="loc_us-gaapMachineryAndEquipmentMember_0" xlink:type="arc" order="1" />
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_OfficeEquipmentMember" xlink:label="loc_us-gaapOfficeEquipmentMember_20" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapPropertyPlantAndEquipmentTypeDomain" xlink:to="loc_us-gaapOfficeEquipmentMember_20" xlink:type="arc" order="21" />
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_FurnitureAndFixturesMember" xlink:label="loc_us-gaapFurnitureAndFixturesMember_40" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapPropertyPlantAndEquipmentTypeDomain" xlink:to="loc_us-gaapFurnitureAndFixturesMember_40" xlink:type="arc" order="41" />
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_LeaseholdImprovementsMember" xlink:label="loc_us-gaapLeaseholdImprovementsMember_60" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapPropertyPlantAndEquipmentTypeDomain" xlink:to="loc_us-gaapLeaseholdImprovementsMember_60" xlink:type="arc" order="61" />
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ConstructionInProgressMember" xlink:label="loc_us-gaapConstructionInProgressMember_80" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapPropertyPlantAndEquipmentTypeDomain" xlink:to="loc_us-gaapConstructionInProgressMember_80" xlink:type="arc" order="81" />
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_PropertyPlantAndEquipmentGross" xlink:label="loc_us-gaapPropertyPlantAndEquipmentGross_130" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapPropertyPlantAndEquipmentLineItems" xlink:to="loc_us-gaapPropertyPlantAndEquipmentGross_130" xlink:type="arc" order="0" />
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_AccumulatedDepreciationDepletionAndAmortizationPropertyPlantAndEquipment" xlink:label="loc_us-gaapAccumulatedDepreciationDepletionAndAmortizationPropertyPlantAndEquipment_130" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapPropertyPlantAndEquipmentLineItems" xlink:to="loc_us-gaapAccumulatedDepreciationDepletionAndAmortizationPropertyPlantAndEquipment_130" xlink:type="arc" order="1" />
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_PropertyPlantAndEquipmentNet" xlink:label="loc_us-gaapPropertyPlantAndEquipmentNet_130" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapPropertyPlantAndEquipmentLineItems" xlink:to="loc_us-gaapPropertyPlantAndEquipmentNet_130" xlink:type="arc" order="2" />
    </link:definitionLink>
    <link:definitionLink xlink:type="extended" xlink:role="http://nanophase.com/role/EquipmentAndLeaseholdImprovementsDetailsNarrative" xlink:title="999049 - Disclosure - Equipment and Leasehold Improvements (Details Narrative)" />
    <link:definitionLink xlink:type="extended" xlink:role="http://nanophase.com/role/QuantitativeInformationRegardingCompanysLeasesIsAsFollowsDetails" xlink:title="999050 - Disclosure - Quantitative information regarding the Company&#8217;s leases is as follows: (Details)" />
    <link:definitionLink xlink:type="extended" xlink:role="http://nanophase.com/role/SupplementalCashFlowInformationRelatedToLeasesIsAsFollowsForYearsEndedDecember312024And2023Details" xlink:title="999051 - Disclosure - Supplemental cash flow information related to leases is as follows for the years ended December 31, 2024 and 2023: (Details)" />
    <link:definitionLink xlink:type="extended" xlink:role="http://nanophase.com/role/FutureMaturitiesOfCompanysOperatingLeasesAsOfDecember312024AreAsFollowsDetails" xlink:title="999052 - Disclosure - The future maturities of the Company&#8217;s operating leases as of December 31, 2024 are as follows: (Details)" />
    <link:definitionLink xlink:type="extended" xlink:role="http://nanophase.com/role/LeaseCommitmentsDetailsNarrative" xlink:title="999053 - Disclosure - Lease Commitments (Details Narrative)" />
    <link:definitionLink xlink:type="extended" xlink:role="http://nanophase.com/role/AccruedExpensesConsistOfFollowingDetails" xlink:title="999054 - Disclosure - Accrued expenses consist of the following: (Details)" />
    <link:definitionLink xlink:type="extended" xlink:role="http://nanophase.com/role/ReconciliationOfIncomeTaxBenefitToAmountComputedByApplyingFederalIncomeTaxRateToLossBeforeProvisionForIncomeTaxesAsOfDecember312024And2023IsAsFollowsDetails" xlink:title="999055 - Disclosure - A reconciliation of income tax benefit to the amount computed by applying the Federal income tax rate to loss before provision for income taxes as of December 31, 2024 and 2023 is as follows: (Details)" />
    <link:definitionLink xlink:type="extended" xlink:role="http://nanophase.com/role/DeferredIncomeTaxesReflectNetTaxEffectsOfTemporaryDifferencesBetweenCarryingAmountsOfAssetsAndLiabilitiesForFinancialReportingPurposesAndAmountsUsedForIncomeTaxPurposes.SignificantComponentsOfOurDeferredIncomeDetails" xlink:title="999056 - Disclosure - Deferred income taxes reflect the net tax effects of temporary differences between the carrying amounts of assets and liabilities for financial reporting purposes and the amounts used for income tax purposes. Significant components of our deferred income  (Details)" />
    <link:definitionLink xlink:type="extended" xlink:role="http://nanophase.com/role/IncomeTaxesDetailsNarrative" xlink:title="999057 - Disclosure - Income Taxes (Details Narrative)">
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_OperatingLossCarryforwardsLineItems" xlink:label="loc_us-gaapOperatingLossCarryforwardsLineItems" />
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_OperatingLossCarryforwardsTable" xlink:label="loc_us-gaapOperatingLossCarryforwardsTable" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xbrldt:contextElement="segment" xlink:from="loc_us-gaapOperatingLossCarryforwardsLineItems" xlink:to="loc_us-gaapOperatingLossCarryforwardsTable" xlink:type="arc" order="10" xbrldt:closed="true" />
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_TaxPeriodAxis" xlink:label="loc_us-gaapTaxPeriodAxis" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaapOperatingLossCarryforwardsTable" xlink:to="loc_us-gaapTaxPeriodAxis" xlink:type="arc" order="1" />
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_TaxPeriodDomain" xlink:label="loc_us-gaapTaxPeriodDomain" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaapTaxPeriodAxis" xlink:to="loc_us-gaapTaxPeriodDomain" xlink:type="arc" order="20" />
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_TaxPeriodDomain" xlink:label="loc_us-gaapTaxPeriodDomain_10" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xbrldt:contextElement="segment" xlink:from="loc_us-gaapTaxPeriodAxis" xlink:to="loc_us-gaapTaxPeriodDomain_10" xlink:type="arc" order="30" />
      <link:loc xlink:type="locator" xlink:href="nanx-20241231.xsd#nanx_Expiring2025To2037Member" xlink:label="loc_nanxExpiring2025To2037Member_40" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapTaxPeriodDomain" xlink:to="loc_nanxExpiring2025To2037Member_40" xlink:type="arc" order="41" />
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_TaxYear2018Member" xlink:label="loc_us-gaapTaxYear2018Member_60" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapTaxPeriodDomain" xlink:to="loc_us-gaapTaxYear2018Member_60" xlink:type="arc" order="61" />
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_IncomeTaxAuthorityAxis" xlink:label="loc_us-gaapIncomeTaxAuthorityAxis" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaapOperatingLossCarryforwardsTable" xlink:to="loc_us-gaapIncomeTaxAuthorityAxis" xlink:type="arc" order="2" />
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_IncomeTaxAuthorityDomain" xlink:label="loc_us-gaapIncomeTaxAuthorityDomain" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaapIncomeTaxAuthorityAxis" xlink:to="loc_us-gaapIncomeTaxAuthorityDomain" xlink:type="arc" order="20" />
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_IncomeTaxAuthorityDomain" xlink:label="loc_us-gaapIncomeTaxAuthorityDomain_10" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xbrldt:contextElement="segment" xlink:from="loc_us-gaapIncomeTaxAuthorityAxis" xlink:to="loc_us-gaapIncomeTaxAuthorityDomain_10" xlink:type="arc" order="30" />
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_DomesticCountryMember" xlink:label="loc_us-gaapDomesticCountryMember_50" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapIncomeTaxAuthorityDomain" xlink:to="loc_us-gaapDomesticCountryMember_50" xlink:type="arc" order="51" />
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_StateAndLocalJurisdictionMember" xlink:label="loc_us-gaapStateAndLocalJurisdictionMember_70" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapIncomeTaxAuthorityDomain" xlink:to="loc_us-gaapStateAndLocalJurisdictionMember_70" xlink:type="arc" order="71" />
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_IncomeTaxExpenseBenefit" xlink:label="loc_us-gaapIncomeTaxExpenseBenefit_100" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapOperatingLossCarryforwardsLineItems" xlink:to="loc_us-gaapIncomeTaxExpenseBenefit_100" xlink:type="arc" order="0" />
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ValuationAllowanceDeferredTaxAssetChangeInAmount" xlink:label="loc_us-gaapValuationAllowanceDeferredTaxAssetChangeInAmount_100" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapOperatingLossCarryforwardsLineItems" xlink:to="loc_us-gaapValuationAllowanceDeferredTaxAssetChangeInAmount_100" xlink:type="arc" order="1" />
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_TaxCreditCarryforwardValuationAllowance" xlink:label="loc_us-gaapTaxCreditCarryforwardValuationAllowance_100" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapOperatingLossCarryforwardsLineItems" xlink:to="loc_us-gaapTaxCreditCarryforwardValuationAllowance_100" xlink:type="arc" order="2" />
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_OperatingLossCarryforwards" xlink:label="loc_us-gaapOperatingLossCarryforwards_100" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapOperatingLossCarryforwardsLineItems" xlink:to="loc_us-gaapOperatingLossCarryforwards_100" xlink:type="arc" order="3" />
      <link:loc xlink:type="locator" xlink:href="nanx-20241231.xsd#nanx_OperatingLossCarryforwardsExpirationYearStart" xlink:label="loc_nanxOperatingLossCarryforwardsExpirationYearStart_100" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapOperatingLossCarryforwardsLineItems" xlink:to="loc_nanxOperatingLossCarryforwardsExpirationYearStart_100" xlink:type="arc" order="4" />
      <link:loc xlink:type="locator" xlink:href="nanx-20241231.xsd#nanx_OperatingLossCarryforwardsExpirationYearEnd" xlink:label="loc_nanxOperatingLossCarryforwardsExpirationYearEnd_100" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapOperatingLossCarryforwardsLineItems" xlink:to="loc_nanxOperatingLossCarryforwardsExpirationYearEnd_100" xlink:type="arc" order="5" />
    </link:definitionLink>
    <link:definitionLink xlink:type="extended" xlink:role="http://nanophase.com/role/CapitalStockDetailsNarrative" xlink:title="999058 - Disclosure - Capital Stock (Details Narrative)">
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ClassOfStockLineItems" xlink:label="loc_us-gaapClassOfStockLineItems" />
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ScheduleOfStockByClassTable" xlink:label="loc_us-gaapScheduleOfStockByClassTable" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xbrldt:contextElement="segment" xlink:from="loc_us-gaapClassOfStockLineItems" xlink:to="loc_us-gaapScheduleOfStockByClassTable" xlink:type="arc" order="10" xbrldt:closed="true" />
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_StatementClassOfStockAxis" xlink:label="loc_us-gaapStatementClassOfStockAxis" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaapScheduleOfStockByClassTable" xlink:to="loc_us-gaapStatementClassOfStockAxis" xlink:type="arc" order="1" />
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ClassOfStockDomain" xlink:label="loc_us-gaapClassOfStockDomain" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaapStatementClassOfStockAxis" xlink:to="loc_us-gaapClassOfStockDomain" xlink:type="arc" order="20" />
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ClassOfStockDomain" xlink:label="loc_us-gaapClassOfStockDomain_10" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xbrldt:contextElement="segment" xlink:from="loc_us-gaapStatementClassOfStockAxis" xlink:to="loc_us-gaapClassOfStockDomain_10" xlink:type="arc" order="30" />
      <link:loc xlink:type="locator" xlink:href="nanx-20241231.xsd#nanx_SeriesXPreferredStockMember" xlink:label="loc_nanxSeriesXPreferredStockMember_20" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapClassOfStockDomain" xlink:to="loc_nanxSeriesXPreferredStockMember_20" xlink:type="arc" order="21" />
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_StatementEquityComponentsAxis" xlink:label="loc_us-gaapStatementEquityComponentsAxis" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaapScheduleOfStockByClassTable" xlink:to="loc_us-gaapStatementEquityComponentsAxis" xlink:type="arc" order="2" />
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_EquityComponentDomain" xlink:label="loc_us-gaapEquityComponentDomain" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaapStatementEquityComponentsAxis" xlink:to="loc_us-gaapEquityComponentDomain" xlink:type="arc" order="20" />
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_EquityComponentDomain" xlink:label="loc_us-gaapEquityComponentDomain_10" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xbrldt:contextElement="segment" xlink:from="loc_us-gaapStatementEquityComponentsAxis" xlink:to="loc_us-gaapEquityComponentDomain_10" xlink:type="arc" order="30" />
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_CommonStockMember" xlink:label="loc_us-gaapCommonStockMember_60" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapEquityComponentDomain" xlink:to="loc_us-gaapCommonStockMember_60" xlink:type="arc" order="61" />
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_PreferredStockSharesAuthorized" xlink:label="loc_us-gaapPreferredStockSharesAuthorized_80" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapClassOfStockLineItems" xlink:to="loc_us-gaapPreferredStockSharesAuthorized_80" xlink:type="arc" order="0" />
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_StockIssuedDuringPeriodSharesNewIssues" xlink:label="loc_us-gaapStockIssuedDuringPeriodSharesNewIssues_80" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapClassOfStockLineItems" xlink:to="loc_us-gaapStockIssuedDuringPeriodSharesNewIssues_80" xlink:type="arc" order="1" />
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_SharesIssuedPricePerShare" xlink:label="loc_us-gaapSharesIssuedPricePerShare_80" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapClassOfStockLineItems" xlink:to="loc_us-gaapSharesIssuedPricePerShare_80" xlink:type="arc" order="2" />
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ProceedsFromIssuanceOfConvertiblePreferredStock" xlink:label="loc_us-gaapProceedsFromIssuanceOfConvertiblePreferredStock_80" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapClassOfStockLineItems" xlink:to="loc_us-gaapProceedsFromIssuanceOfConvertiblePreferredStock_80" xlink:type="arc" order="3" />
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_CommonStockParOrStatedValuePerShare" xlink:label="loc_us-gaapCommonStockParOrStatedValuePerShare_80" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapClassOfStockLineItems" xlink:to="loc_us-gaapCommonStockParOrStatedValuePerShare_80" xlink:type="arc" order="4" />
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_CommonStockSharesAuthorized" xlink:label="loc_us-gaapCommonStockSharesAuthorized_80" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapClassOfStockLineItems" xlink:to="loc_us-gaapCommonStockSharesAuthorized_80" xlink:type="arc" order="5" />
      <link:loc xlink:type="locator" xlink:href="nanx-20241231.xsd#nanx_CommonStockSharesAuthorizedForConversionOfPreferredStock" xlink:label="loc_nanxCommonStockSharesAuthorizedForConversionOfPreferredStock_80" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapClassOfStockLineItems" xlink:to="loc_nanxCommonStockSharesAuthorizedForConversionOfPreferredStock_80" xlink:type="arc" order="6" />
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ConvertiblePreferredStockSharesIssuedUponConversion" xlink:label="loc_us-gaapConvertiblePreferredStockSharesIssuedUponConversion_80" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapClassOfStockLineItems" xlink:to="loc_us-gaapConvertiblePreferredStockSharesIssuedUponConversion_80" xlink:type="arc" order="7" />
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_PreferredStockConvertibleConversionPrice" xlink:label="loc_us-gaapPreferredStockConvertibleConversionPrice_80" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapClassOfStockLineItems" xlink:to="loc_us-gaapPreferredStockConvertibleConversionPrice_80" xlink:type="arc" order="8" />
      <link:loc xlink:type="locator" xlink:href="nanx-20241231.xsd#nanx_PreferredStockConvertibleInterestRateForUnpaidRedemption" xlink:label="loc_nanxPreferredStockConvertibleInterestRateForUnpaidRedemption_80" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapClassOfStockLineItems" xlink:to="loc_nanxPreferredStockConvertibleInterestRateForUnpaidRedemption_80" xlink:type="arc" order="9" />
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_PreferredStockLiquidationPreference" xlink:label="loc_us-gaapPreferredStockLiquidationPreference_80" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapClassOfStockLineItems" xlink:to="loc_us-gaapPreferredStockLiquidationPreference_80" xlink:type="arc" order="10" />
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ConversionOfStockSharesConverted1" xlink:label="loc_us-gaapConversionOfStockSharesConverted1_80" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapClassOfStockLineItems" xlink:to="loc_us-gaapConversionOfStockSharesConverted1_80" xlink:type="arc" order="11" />
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ConversionOfStockSharesIssued1" xlink:label="loc_us-gaapConversionOfStockSharesIssued1_80" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapClassOfStockLineItems" xlink:to="loc_us-gaapConversionOfStockSharesIssued1_80" xlink:type="arc" order="12" />
    </link:definitionLink>
    <link:definitionLink xlink:type="extended" xlink:role="http://nanophase.com/role/WeFollowAscTopic718Share-basedPaymentsInWhichCompensationExpenseIsRecognizedOnlyForShare-basedPaymentsExpectedToVest.Details" xlink:title="999059 - Disclosure - We follow ASC Topic 718, Share-Based Payments, in which compensation expense is recognized only for share-based payments expected to vest. (Details)">
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems" xlink:label="loc_us-gaapShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems" />
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable" xlink:label="loc_us-gaapScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xbrldt:contextElement="segment" xlink:from="loc_us-gaapShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems" xlink:to="loc_us-gaapScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable" xlink:type="arc" order="10" xbrldt:closed="true" />
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_AwardTypeAxis" xlink:label="loc_us-gaapAwardTypeAxis" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaapScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable" xlink:to="loc_us-gaapAwardTypeAxis" xlink:type="arc" order="1" />
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain" xlink:label="loc_us-gaapShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaapAwardTypeAxis" xlink:to="loc_us-gaapShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain" xlink:type="arc" order="20" />
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain" xlink:label="loc_us-gaapShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_10" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xbrldt:contextElement="segment" xlink:from="loc_us-gaapAwardTypeAxis" xlink:to="loc_us-gaapShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_10" xlink:type="arc" order="30" />
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_EmployeeStockOptionMember" xlink:label="loc_us-gaapEmployeeStockOptionMember_0" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain" xlink:to="loc_us-gaapEmployeeStockOptionMember_0" xlink:type="arc" order="1" />
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_StockOptionPlanExpense" xlink:label="loc_us-gaapStockOptionPlanExpense_50" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems" xlink:to="loc_us-gaapStockOptionPlanExpense_50" xlink:type="arc" order="0" />
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognized" xlink:label="loc_us-gaapEmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognized_50" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems" xlink:to="loc_us-gaapEmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognized_50" xlink:type="arc" order="1" />
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognizedPeriodForRecognition1" xlink:label="loc_us-gaapEmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognizedPeriodForRecognition1_50" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems" xlink:to="loc_us-gaapEmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognizedPeriodForRecognition1_50" xlink:type="arc" order="2" />
    </link:definitionLink>
    <link:definitionLink xlink:type="extended" xlink:role="http://nanophase.com/role/FollowingTableIllustratesVariousAssumptionsUsedToCalculateBlack-scholesOptionPricingModelForOptionsGrantedForAllYearsPresentedDetails" xlink:title="999060 - Disclosure - The following table illustrates the various assumptions used to calculate the Black-Scholes option pricing model for options granted for all years presented: (Details)" />
    <link:definitionLink xlink:type="extended" xlink:role="http://nanophase.com/role/AdditionalDisclosuresForOptionsGrantedForAllYearsPresentedDetails" xlink:title="999061 - Disclosure - Additional disclosures for options granted for all years presented: (Details)">
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems" xlink:label="loc_us-gaapShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems" />
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable" xlink:label="loc_us-gaapScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xbrldt:contextElement="segment" xlink:from="loc_us-gaapShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems" xlink:to="loc_us-gaapScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable" xlink:type="arc" order="10" xbrldt:closed="true" />
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_AwardTypeAxis" xlink:label="loc_us-gaapAwardTypeAxis" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaapScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable" xlink:to="loc_us-gaapAwardTypeAxis" xlink:type="arc" order="1" />
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain" xlink:label="loc_us-gaapShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaapAwardTypeAxis" xlink:to="loc_us-gaapShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain" xlink:type="arc" order="20" />
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain" xlink:label="loc_us-gaapShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_10" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xbrldt:contextElement="segment" xlink:from="loc_us-gaapAwardTypeAxis" xlink:to="loc_us-gaapShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_10" xlink:type="arc" order="30" />
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_EmployeeStockOptionMember" xlink:label="loc_us-gaapEmployeeStockOptionMember_0" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain" xlink:to="loc_us-gaapEmployeeStockOptionMember_0" xlink:type="arc" order="1" />
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardAwardVestingPeriod1" xlink:label="loc_us-gaapShareBasedCompensationArrangementByShareBasedPaymentAwardAwardVestingPeriod1_30" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems" xlink:to="loc_us-gaapShareBasedCompensationArrangementByShareBasedPaymentAwardAwardVestingPeriod1_30" xlink:type="arc" order="0" />
      <link:loc xlink:type="locator" xlink:href="nanx-20241231.xsd#nanx_ShareBasedCompensationArrangementByShareBasedPaymentAwardAwardContractualLife" xlink:label="loc_nanxShareBasedCompensationArrangementByShareBasedPaymentAwardAwardContractualLife_30" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems" xlink:to="loc_nanxShareBasedCompensationArrangementByShareBasedPaymentAwardAwardContractualLife_30" xlink:type="arc" order="1" />
      <link:loc xlink:type="locator" xlink:href="nanx-20241231.xsd#nanx_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsFortfeitureRate" xlink:label="loc_nanxShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsFortfeitureRate_30" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems" xlink:to="loc_nanxShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsFortfeitureRate_30" xlink:type="arc" order="2" />
    </link:definitionLink>
    <link:definitionLink xlink:type="extended" xlink:role="http://nanophase.com/role/FollowingTableSummarizesOptionActivityForOurEmployeesAndDirectorsDuringYearEndedDecember312024Details" xlink:title="999062 - Disclosure - The following table summarizes the option activity for our employees and directors during the year ended December 31, 2024: (Details)" />
    <link:definitionLink xlink:type="extended" xlink:role="http://nanophase.com/role/AggregateIntrinsicValueInTableAboveIsBasedOnOurClosingStockPriceOf2.26Details" xlink:title="999063 - Disclosure - The aggregate intrinsic value in the table above is based on our closing stock price of $2.26 (Details)">
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems" xlink:label="loc_us-gaapShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems" />
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable" xlink:label="loc_us-gaapScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xbrldt:contextElement="segment" xlink:from="loc_us-gaapShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems" xlink:to="loc_us-gaapScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable" xlink:type="arc" order="10" xbrldt:closed="true" />
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_AwardTypeAxis" xlink:label="loc_us-gaapAwardTypeAxis" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaapScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable" xlink:to="loc_us-gaapAwardTypeAxis" xlink:type="arc" order="1" />
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain" xlink:label="loc_us-gaapShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaapAwardTypeAxis" xlink:to="loc_us-gaapShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain" xlink:type="arc" order="20" />
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain" xlink:label="loc_us-gaapShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_10" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xbrldt:contextElement="segment" xlink:from="loc_us-gaapAwardTypeAxis" xlink:to="loc_us-gaapShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_10" xlink:type="arc" order="30" />
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_EmployeeStockOptionMember" xlink:label="loc_us-gaapEmployeeStockOptionMember_0" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain" xlink:to="loc_us-gaapEmployeeStockOptionMember_0" xlink:type="arc" order="1" />
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_SharePrice" xlink:label="loc_us-gaapSharePrice_40" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems" xlink:to="loc_us-gaapSharePrice_40" xlink:type="arc" order="0" />
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_StockIssuedDuringPeriodSharesStockOptionsExercised" xlink:label="loc_us-gaapStockIssuedDuringPeriodSharesStockOptionsExercised_40" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems" xlink:to="loc_us-gaapStockIssuedDuringPeriodSharesStockOptionsExercised_40" xlink:type="arc" order="1" />
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsExercisesInPeriodTotalIntrinsicValue" xlink:label="loc_us-gaapShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsExercisesInPeriodTotalIntrinsicValue_40" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems" xlink:to="loc_us-gaapShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsExercisesInPeriodTotalIntrinsicValue_40" xlink:type="arc" order="2" />
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ProceedsFromStockOptionsExercised" xlink:label="loc_us-gaapProceedsFromStockOptionsExercised_40" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems" xlink:to="loc_us-gaapProceedsFromStockOptionsExercised_40" xlink:type="arc" order="3" />
    </link:definitionLink>
    <link:definitionLink xlink:type="extended" xlink:role="http://nanophase.com/role/StockOptionsAndStockGrantsDetailsNarrative" xlink:title="999064 - Disclosure - Stock Options and Stock Grants (Details Narrative)">
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems" xlink:label="loc_us-gaapShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems" />
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable" xlink:label="loc_us-gaapScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xbrldt:contextElement="segment" xlink:from="loc_us-gaapShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems" xlink:to="loc_us-gaapScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable" xlink:type="arc" order="10" xbrldt:closed="true" />
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_AwardTypeAxis" xlink:label="loc_us-gaapAwardTypeAxis" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaapScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable" xlink:to="loc_us-gaapAwardTypeAxis" xlink:type="arc" order="1" />
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain" xlink:label="loc_us-gaapShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaapAwardTypeAxis" xlink:to="loc_us-gaapShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain" xlink:type="arc" order="20" />
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain" xlink:label="loc_us-gaapShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_10" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xbrldt:contextElement="segment" xlink:from="loc_us-gaapAwardTypeAxis" xlink:to="loc_us-gaapShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_10" xlink:type="arc" order="30" />
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_EmployeeStockOptionMember" xlink:label="loc_us-gaapEmployeeStockOptionMember_0" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain" xlink:to="loc_us-gaapEmployeeStockOptionMember_0" xlink:type="arc" order="1" />
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_PlanNameAxis" xlink:label="loc_us-gaapPlanNameAxis" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaapScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable" xlink:to="loc_us-gaapPlanNameAxis" xlink:type="arc" order="2" />
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_PlanNameDomain" xlink:label="loc_us-gaapPlanNameDomain" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaapPlanNameAxis" xlink:to="loc_us-gaapPlanNameDomain" xlink:type="arc" order="20" />
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_PlanNameDomain" xlink:label="loc_us-gaapPlanNameDomain_10" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xbrldt:contextElement="segment" xlink:from="loc_us-gaapPlanNameAxis" xlink:to="loc_us-gaapPlanNameDomain_10" xlink:type="arc" order="30" />
      <link:loc xlink:type="locator" xlink:href="nanx-20241231.xsd#nanx_PriorTo2019PlanMember" xlink:label="loc_nanxPriorTo2019PlanMember_0" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapPlanNameDomain" xlink:to="loc_nanxPriorTo2019PlanMember_0" xlink:type="arc" order="2" />
      <link:loc xlink:type="locator" xlink:href="nanx-20241231.xsd#nanx_Options2019PlanMember" xlink:label="loc_nanxOptions2019PlanMember_10" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapPlanNameDomain" xlink:to="loc_nanxOptions2019PlanMember_10" xlink:type="arc" order="12" />
      <link:loc xlink:type="locator" xlink:href="nanx-20241231.xsd#nanx_Options2010PlanMember" xlink:label="loc_nanxOptions2010PlanMember_20" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapPlanNameDomain" xlink:to="loc_nanxOptions2010PlanMember_20" xlink:type="arc" order="22" />
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardExpirationPeriod" xlink:label="loc_us-gaapSharebasedCompensationArrangementBySharebasedPaymentAwardExpirationPeriod_40" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems" xlink:to="loc_us-gaapSharebasedCompensationArrangementBySharebasedPaymentAwardExpirationPeriod_40" xlink:type="arc" order="0" />
    </link:definitionLink>
    <link:definitionLink xlink:type="extended" xlink:role="http://nanophase.com/role/KProfit-sharingPlanDetailsNarrative" xlink:title="999065 - Disclosure - 401(k) Profit-Sharing Plan (Details Narrative)" />
    <link:definitionLink xlink:type="extended" xlink:role="http://nanophase.com/role/RevenuesFromTheseThreeCustomersAsPercentageOfTotalCompanyRevenueWasApproximatelyDetails" xlink:title="999066 - Disclosure - Revenues from these three customers, as a percentage of total Company revenue, was approximately: (Details)">
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ConcentrationRiskLineItems" xlink:label="loc_us-gaapConcentrationRiskLineItems" />
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ConcentrationRiskTable" xlink:label="loc_us-gaapConcentrationRiskTable" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xbrldt:contextElement="segment" xlink:from="loc_us-gaapConcentrationRiskLineItems" xlink:to="loc_us-gaapConcentrationRiskTable" xlink:type="arc" order="10" xbrldt:closed="true" />
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/srt/2024/elts/srt-2024.xsd#srt_MajorCustomersAxis" xlink:label="loc_srtMajorCustomersAxis" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaapConcentrationRiskTable" xlink:to="loc_srtMajorCustomersAxis" xlink:type="arc" order="1" />
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/srt/2024/elts/srt-2024.xsd#srt_NameOfMajorCustomerDomain" xlink:label="loc_srtNameOfMajorCustomerDomain" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srtMajorCustomersAxis" xlink:to="loc_srtNameOfMajorCustomerDomain" xlink:type="arc" order="20" />
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/srt/2024/elts/srt-2024.xsd#srt_NameOfMajorCustomerDomain" xlink:label="loc_srtNameOfMajorCustomerDomain_10" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xbrldt:contextElement="segment" xlink:from="loc_srtMajorCustomersAxis" xlink:to="loc_srtNameOfMajorCustomerDomain_10" xlink:type="arc" order="30" />
      <link:loc xlink:type="locator" xlink:href="nanx-20241231.xsd#nanx_CustomerOneMember" xlink:label="loc_nanxCustomerOneMember_0" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srtNameOfMajorCustomerDomain" xlink:to="loc_nanxCustomerOneMember_0" xlink:type="arc" order="1" />
      <link:loc xlink:type="locator" xlink:href="nanx-20241231.xsd#nanx_CustomerTwoMember" xlink:label="loc_nanxCustomerTwoMember_20" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srtNameOfMajorCustomerDomain" xlink:to="loc_nanxCustomerTwoMember_20" xlink:type="arc" order="21" />
      <link:loc xlink:type="locator" xlink:href="nanx-20241231.xsd#nanx_CustomerThreeMember" xlink:label="loc_nanxCustomerThreeMember_40" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srtNameOfMajorCustomerDomain" xlink:to="loc_nanxCustomerThreeMember_40" xlink:type="arc" order="41" />
      <link:loc xlink:type="locator" xlink:href="nanx-20241231.xsd#nanx_CustomersOneThroughThreeMember" xlink:label="loc_nanxCustomersOneThroughThreeMember_60" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srtNameOfMajorCustomerDomain" xlink:to="loc_nanxCustomersOneThroughThreeMember_60" xlink:type="arc" order="61" />
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ConcentrationRiskByTypeAxis" xlink:label="loc_us-gaapConcentrationRiskByTypeAxis" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaapConcentrationRiskTable" xlink:to="loc_us-gaapConcentrationRiskByTypeAxis" xlink:type="arc" order="2" />
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ConcentrationRiskTypeDomain" xlink:label="loc_us-gaapConcentrationRiskTypeDomain" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaapConcentrationRiskByTypeAxis" xlink:to="loc_us-gaapConcentrationRiskTypeDomain" xlink:type="arc" order="20" />
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ConcentrationRiskTypeDomain" xlink:label="loc_us-gaapConcentrationRiskTypeDomain_10" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xbrldt:contextElement="segment" xlink:from="loc_us-gaapConcentrationRiskByTypeAxis" xlink:to="loc_us-gaapConcentrationRiskTypeDomain_10" xlink:type="arc" order="30" />
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_CustomerConcentrationRiskMember" xlink:label="loc_us-gaapCustomerConcentrationRiskMember_0" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapConcentrationRiskTypeDomain" xlink:to="loc_us-gaapCustomerConcentrationRiskMember_0" xlink:type="arc" order="2" />
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ConcentrationRiskByBenchmarkAxis" xlink:label="loc_us-gaapConcentrationRiskByBenchmarkAxis" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaapConcentrationRiskTable" xlink:to="loc_us-gaapConcentrationRiskByBenchmarkAxis" xlink:type="arc" order="3" />
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ConcentrationRiskBenchmarkDomain" xlink:label="loc_us-gaapConcentrationRiskBenchmarkDomain" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaapConcentrationRiskByBenchmarkAxis" xlink:to="loc_us-gaapConcentrationRiskBenchmarkDomain" xlink:type="arc" order="20" />
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ConcentrationRiskBenchmarkDomain" xlink:label="loc_us-gaapConcentrationRiskBenchmarkDomain_10" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xbrldt:contextElement="segment" xlink:from="loc_us-gaapConcentrationRiskByBenchmarkAxis" xlink:to="loc_us-gaapConcentrationRiskBenchmarkDomain_10" xlink:type="arc" order="30" />
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_SalesRevenueNetMember" xlink:label="loc_us-gaapSalesRevenueNetMember_0" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapConcentrationRiskBenchmarkDomain" xlink:to="loc_us-gaapSalesRevenueNetMember_0" xlink:type="arc" order="3" />
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ConcentrationRiskPercentage1" xlink:label="loc_us-gaapConcentrationRiskPercentage1_90" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapConcentrationRiskLineItems" xlink:to="loc_us-gaapConcentrationRiskPercentage1_90" xlink:type="arc" order="0" />
    </link:definitionLink>
    <link:definitionLink xlink:type="extended" xlink:role="http://nanophase.com/role/AccountsReceivableBalancesForTheseThreeCustomersAsPercentageOfTotalCompanyAccountsReceivableWasApproximatelyDetails" xlink:title="999067 - Disclosure - Accounts receivable balances for these three customers, as a percentage of total Company accounts receivable, was approximately: (Details)">
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_StatementLineItems" xlink:label="loc_us-gaapStatementLineItems" />
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_StatementTable" xlink:label="loc_us-gaapStatementTable" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xbrldt:contextElement="segment" xlink:from="loc_us-gaapStatementLineItems" xlink:to="loc_us-gaapStatementTable" xlink:type="arc" order="10" xbrldt:closed="true" />
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/srt/2024/elts/srt-2024.xsd#srt_MajorCustomersAxis" xlink:label="loc_srtMajorCustomersAxis" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaapStatementTable" xlink:to="loc_srtMajorCustomersAxis" xlink:type="arc" order="1" />
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/srt/2024/elts/srt-2024.xsd#srt_NameOfMajorCustomerDomain" xlink:label="loc_srtNameOfMajorCustomerDomain" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srtMajorCustomersAxis" xlink:to="loc_srtNameOfMajorCustomerDomain" xlink:type="arc" order="20" />
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/srt/2024/elts/srt-2024.xsd#srt_NameOfMajorCustomerDomain" xlink:label="loc_srtNameOfMajorCustomerDomain_10" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xbrldt:contextElement="segment" xlink:from="loc_srtMajorCustomersAxis" xlink:to="loc_srtNameOfMajorCustomerDomain_10" xlink:type="arc" order="30" />
      <link:loc xlink:type="locator" xlink:href="nanx-20241231.xsd#nanx_CustomerOneMember" xlink:label="loc_nanxCustomerOneMember_0" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srtNameOfMajorCustomerDomain" xlink:to="loc_nanxCustomerOneMember_0" xlink:type="arc" order="1" />
      <link:loc xlink:type="locator" xlink:href="nanx-20241231.xsd#nanx_CustomerTwoMember" xlink:label="loc_nanxCustomerTwoMember_20" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srtNameOfMajorCustomerDomain" xlink:to="loc_nanxCustomerTwoMember_20" xlink:type="arc" order="21" />
      <link:loc xlink:type="locator" xlink:href="nanx-20241231.xsd#nanx_CustomerThreeMember" xlink:label="loc_nanxCustomerThreeMember_40" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srtNameOfMajorCustomerDomain" xlink:to="loc_nanxCustomerThreeMember_40" xlink:type="arc" order="41" />
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ContractWithCustomerReceivableAfterAllowanceForCreditLossCurrent" xlink:label="loc_us-gaapContractWithCustomerReceivableAfterAllowanceForCreditLossCurrent_90" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapStatementLineItems" xlink:to="loc_us-gaapContractWithCustomerReceivableAfterAllowanceForCreditLossCurrent_90" xlink:type="arc" order="0" />
    </link:definitionLink>
    <link:definitionLink xlink:type="extended" xlink:role="http://nanophase.com/role/SignificantCustomersDetailsNarrative" xlink:title="999068 - Disclosure - Significant Customers (Details Narrative)">
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_SupplyCommitmentLineItems" xlink:label="loc_us-gaapSupplyCommitmentLineItems" />
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_SupplyCommitmentTable" xlink:label="loc_us-gaapSupplyCommitmentTable" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xbrldt:contextElement="segment" xlink:from="loc_us-gaapSupplyCommitmentLineItems" xlink:to="loc_us-gaapSupplyCommitmentTable" xlink:type="arc" order="10" xbrldt:closed="true" />
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_SupplyCommitmentAxis" xlink:label="loc_us-gaapSupplyCommitmentAxis" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaapSupplyCommitmentTable" xlink:to="loc_us-gaapSupplyCommitmentAxis" xlink:type="arc" order="1" />
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_SupplyCommitmentArrangementMember" xlink:label="loc_us-gaapSupplyCommitmentArrangementMember" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaapSupplyCommitmentAxis" xlink:to="loc_us-gaapSupplyCommitmentArrangementMember" xlink:type="arc" order="20" />
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_SupplyCommitmentArrangementMember" xlink:label="loc_us-gaapSupplyCommitmentArrangementMember_10" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xbrldt:contextElement="segment" xlink:from="loc_us-gaapSupplyCommitmentAxis" xlink:to="loc_us-gaapSupplyCommitmentArrangementMember_10" xlink:type="arc" order="30" />
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_SupplyCommitmentMember" xlink:label="loc_us-gaapSupplyCommitmentMember_0" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapSupplyCommitmentArrangementMember" xlink:to="loc_us-gaapSupplyCommitmentMember_0" xlink:type="arc" order="1" />
      <link:loc xlink:type="locator" xlink:href="nanx-20241231.xsd#nanx_EquipmentSaleNetBookValueEquipment" xlink:label="loc_nanxEquipmentSaleNetBookValueEquipment_20" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapSupplyCommitmentLineItems" xlink:to="loc_nanxEquipmentSaleNetBookValueEquipment_20" xlink:type="arc" order="0" />
      <link:loc xlink:type="locator" xlink:href="nanx-20241231.xsd#nanx_EquipmentSaleOriginalBookValueOfEquipmentAndUpgrades" xlink:label="loc_nanxEquipmentSaleOriginalBookValueOfEquipmentAndUpgrades_20" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapSupplyCommitmentLineItems" xlink:to="loc_nanxEquipmentSaleOriginalBookValueOfEquipmentAndUpgrades_20" xlink:type="arc" order="1" />
    </link:definitionLink>
    <link:definitionLink xlink:type="extended" xlink:role="http://nanophase.com/role/ChiefOperatingDecisionMakerUsesGrossProfitAndNetIncomeToEvaluateCompanyPerformanceAndInWhatWayToAllocateResources.SignificantSegmentExpensesWhichAreSameAsEntityAsWholeAreAsFollowsDetails" xlink:title="999069 - Disclosure - The Chief Operating Decision Maker uses gross profit and net income to evaluate Company performance and in what way to allocate resources. Significant segment expenses, which are the same as the entity as a whole, are as follows: (Details)">
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_InterimPeriodCostsNotAllocableLineItems" xlink:label="loc_us-gaapInterimPeriodCostsNotAllocableLineItems" />
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_InterimPeriodCostsNotAllocableTable" xlink:label="loc_us-gaapInterimPeriodCostsNotAllocableTable" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xbrldt:contextElement="segment" xlink:from="loc_us-gaapInterimPeriodCostsNotAllocableLineItems" xlink:to="loc_us-gaapInterimPeriodCostsNotAllocableTable" xlink:type="arc" order="10" xbrldt:closed="true" />
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_NatureOfExpenseAxis" xlink:label="loc_us-gaapNatureOfExpenseAxis" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaapInterimPeriodCostsNotAllocableTable" xlink:to="loc_us-gaapNatureOfExpenseAxis" xlink:type="arc" order="1" />
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_InterimPeriodCostsNotAllocableDomain" xlink:label="loc_us-gaapInterimPeriodCostsNotAllocableDomain" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaapNatureOfExpenseAxis" xlink:to="loc_us-gaapInterimPeriodCostsNotAllocableDomain" xlink:type="arc" order="20" />
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_InterimPeriodCostsNotAllocableDomain" xlink:label="loc_us-gaapInterimPeriodCostsNotAllocableDomain_10" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xbrldt:contextElement="segment" xlink:from="loc_us-gaapNatureOfExpenseAxis" xlink:to="loc_us-gaapInterimPeriodCostsNotAllocableDomain_10" xlink:type="arc" order="30" />
      <link:loc xlink:type="locator" xlink:href="nanx-20241231.xsd#nanx_EmployeeCostsMember" xlink:label="loc_nanxEmployeeCostsMember_20" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapInterimPeriodCostsNotAllocableDomain" xlink:to="loc_nanxEmployeeCostsMember_20" xlink:type="arc" order="21" />
      <link:loc xlink:type="locator" xlink:href="nanx-20241231.xsd#nanx_ContractorsAndProfessionalServicesMember" xlink:label="loc_nanxContractorsAndProfessionalServicesMember_40" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapInterimPeriodCostsNotAllocableDomain" xlink:to="loc_nanxContractorsAndProfessionalServicesMember_40" xlink:type="arc" order="41" />
      <link:loc xlink:type="locator" xlink:href="nanx-20241231.xsd#nanx_MaterialsAndSuppliesMember" xlink:label="loc_nanxMaterialsAndSuppliesMember_60" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapInterimPeriodCostsNotAllocableDomain" xlink:to="loc_nanxMaterialsAndSuppliesMember_60" xlink:type="arc" order="61" />
      <link:loc xlink:type="locator" xlink:href="nanx-20241231.xsd#nanx_DepreciationMember" xlink:label="loc_nanxDepreciationMember_80" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapInterimPeriodCostsNotAllocableDomain" xlink:to="loc_nanxDepreciationMember_80" xlink:type="arc" order="81" />
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_InterestExpenseMember" xlink:label="loc_us-gaapInterestExpenseMember_100" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapInterimPeriodCostsNotAllocableDomain" xlink:to="loc_us-gaapInterestExpenseMember_100" xlink:type="arc" order="101" />
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_OtherIncomeMember" xlink:label="loc_us-gaapOtherIncomeMember_120" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapInterimPeriodCostsNotAllocableDomain" xlink:to="loc_us-gaapOtherIncomeMember_120" xlink:type="arc" order="121" />
      <link:loc xlink:type="locator" xlink:href="nanx-20241231.xsd#nanx_TaxExpenseMember" xlink:label="loc_nanxTaxExpenseMember_140" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapInterimPeriodCostsNotAllocableDomain" xlink:to="loc_nanxTaxExpenseMember_140" xlink:type="arc" order="141" />
      <link:loc xlink:type="locator" xlink:href="nanx-20241231.xsd#nanx_FacilitiesMember" xlink:label="loc_nanxFacilitiesMember_160" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapInterimPeriodCostsNotAllocableDomain" xlink:to="loc_nanxFacilitiesMember_160" xlink:type="arc" order="161" />
      <link:loc xlink:type="locator" xlink:href="nanx-20241231.xsd#nanx_ShippingMember" xlink:label="loc_nanxShippingMember_180" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapInterimPeriodCostsNotAllocableDomain" xlink:to="loc_nanxShippingMember_180" xlink:type="arc" order="181" />
      <link:loc xlink:type="locator" xlink:href="nanx-20241231.xsd#nanx_TestingMember" xlink:label="loc_nanxTestingMember_200" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapInterimPeriodCostsNotAllocableDomain" xlink:to="loc_nanxTestingMember_200" xlink:type="arc" order="201" />
      <link:loc xlink:type="locator" xlink:href="nanx-20241231.xsd#nanx_ITServicesMember" xlink:label="loc_nanxITServicesMember_220" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapInterimPeriodCostsNotAllocableDomain" xlink:to="loc_nanxITServicesMember_220" xlink:type="arc" order="221" />
      <link:loc xlink:type="locator" xlink:href="nanx-20241231.xsd#nanx_InsuranceMember" xlink:label="loc_nanxInsuranceMember_240" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapInterimPeriodCostsNotAllocableDomain" xlink:to="loc_nanxInsuranceMember_240" xlink:type="arc" order="241" />
      <link:loc xlink:type="locator" xlink:href="nanx-20241231.xsd#nanx_ManufacturingOtherExpenseMember" xlink:label="loc_nanxManufacturingOtherExpenseMember_260" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapInterimPeriodCostsNotAllocableDomain" xlink:to="loc_nanxManufacturingOtherExpenseMember_260" xlink:type="arc" order="261" />
      <link:loc xlink:type="locator" xlink:href="nanx-20241231.xsd#nanx_SellingGeneralAndAdministrativeOtherExpenseMember" xlink:label="loc_nanxSellingGeneralAndAdministrativeOtherExpenseMember_280" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapInterimPeriodCostsNotAllocableDomain" xlink:to="loc_nanxSellingGeneralAndAdministrativeOtherExpenseMember_280" xlink:type="arc" order="281" />
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_RevenueFromContractWithCustomerExcludingAssessedTax" xlink:label="loc_us-gaapRevenueFromContractWithCustomerExcludingAssessedTax_310" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapInterimPeriodCostsNotAllocableLineItems" xlink:to="loc_us-gaapRevenueFromContractWithCustomerExcludingAssessedTax_310" xlink:type="arc" order="0" />
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_CostsAndExpenses" xlink:label="loc_us-gaapCostsAndExpenses_310" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapInterimPeriodCostsNotAllocableLineItems" xlink:to="loc_us-gaapCostsAndExpenses_310" xlink:type="arc" order="1" />
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_NetIncomeLoss" xlink:label="loc_us-gaapNetIncomeLoss_310" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapInterimPeriodCostsNotAllocableLineItems" xlink:to="loc_us-gaapNetIncomeLoss_310" xlink:type="arc" order="2" />
    </link:definitionLink>
    <link:definitionLink xlink:type="extended" xlink:role="http://nanophase.com/role/RevenuesFor2024And2023ByCategoryAreAsFollowsDetails" xlink:title="999070 - Disclosure - The revenues for 2024 and 2023 by category are as follows: (Details)">
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_EntityWideInformationRevenueFromExternalCustomerLineItems" xlink:label="loc_us-gaapEntityWideInformationRevenueFromExternalCustomerLineItems" />
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ScheduleOfEntityWideInformationRevenueFromExternalCustomersByProductsAndServicesTable" xlink:label="loc_us-gaapScheduleOfEntityWideInformationRevenueFromExternalCustomersByProductsAndServicesTable" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xbrldt:contextElement="segment" xlink:from="loc_us-gaapEntityWideInformationRevenueFromExternalCustomerLineItems" xlink:to="loc_us-gaapScheduleOfEntityWideInformationRevenueFromExternalCustomersByProductsAndServicesTable" xlink:type="arc" order="10" xbrldt:closed="true" />
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/srt/2024/elts/srt-2024.xsd#srt_ProductOrServiceAxis" xlink:label="loc_srtProductOrServiceAxis" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaapScheduleOfEntityWideInformationRevenueFromExternalCustomersByProductsAndServicesTable" xlink:to="loc_srtProductOrServiceAxis" xlink:type="arc" order="1" />
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/srt/2024/elts/srt-2024.xsd#srt_ProductsAndServicesDomain" xlink:label="loc_srtProductsAndServicesDomain" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srtProductOrServiceAxis" xlink:to="loc_srtProductsAndServicesDomain" xlink:type="arc" order="20" />
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/srt/2024/elts/srt-2024.xsd#srt_ProductsAndServicesDomain" xlink:label="loc_srtProductsAndServicesDomain_10" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xbrldt:contextElement="segment" xlink:from="loc_srtProductOrServiceAxis" xlink:to="loc_srtProductsAndServicesDomain_10" xlink:type="arc" order="30" />
      <link:loc xlink:type="locator" xlink:href="nanx-20241231.xsd#nanx_ConsumerProductsMember" xlink:label="loc_nanxConsumerProductsMember_0" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srtProductsAndServicesDomain" xlink:to="loc_nanxConsumerProductsMember_0" xlink:type="arc" order="1" />
      <link:loc xlink:type="locator" xlink:href="nanx-20241231.xsd#nanx_PersonalCareIngredientsMember" xlink:label="loc_nanxPersonalCareIngredientsMember_20" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srtProductsAndServicesDomain" xlink:to="loc_nanxPersonalCareIngredientsMember_20" xlink:type="arc" order="21" />
      <link:loc xlink:type="locator" xlink:href="nanx-20241231.xsd#nanx_AdvancedMaterialsMember" xlink:label="loc_nanxAdvancedMaterialsMember_40" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srtProductsAndServicesDomain" xlink:to="loc_nanxAdvancedMaterialsMember_40" xlink:type="arc" order="41" />
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_RevenueFromContractWithCustomerExcludingAssessedTax" xlink:label="loc_us-gaapRevenueFromContractWithCustomerExcludingAssessedTax_90" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapEntityWideInformationRevenueFromExternalCustomerLineItems" xlink:to="loc_us-gaapRevenueFromContractWithCustomerExcludingAssessedTax_90" xlink:type="arc" order="0" />
    </link:definitionLink>
    <link:definitionLink xlink:type="extended" xlink:role="http://nanophase.com/role/BusinessSegmentationAndGeographicalDistributionDetailsNarrative" xlink:title="999071 - Disclosure - Business Segmentation and Geographical Distribution (Details Narrative)">
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_RevenuesFromExternalCustomersAndLongLivedAssetsLineItems" xlink:label="loc_us-gaapRevenuesFromExternalCustomersAndLongLivedAssetsLineItems" />
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ScheduleOfRevenuesFromExternalCustomersAndLongLivedAssetsTable" xlink:label="loc_us-gaapScheduleOfRevenuesFromExternalCustomersAndLongLivedAssetsTable" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xbrldt:contextElement="segment" xlink:from="loc_us-gaapRevenuesFromExternalCustomersAndLongLivedAssetsLineItems" xlink:to="loc_us-gaapScheduleOfRevenuesFromExternalCustomersAndLongLivedAssetsTable" xlink:type="arc" order="10" xbrldt:closed="true" />
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/srt/2024/elts/srt-2024.xsd#srt_StatementGeographicalAxis" xlink:label="loc_srtStatementGeographicalAxis" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaapScheduleOfRevenuesFromExternalCustomersAndLongLivedAssetsTable" xlink:to="loc_srtStatementGeographicalAxis" xlink:type="arc" order="1" />
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/srt/2024/elts/srt-2024.xsd#srt_SegmentGeographicalDomain" xlink:label="loc_srtSegmentGeographicalDomain" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srtStatementGeographicalAxis" xlink:to="loc_srtSegmentGeographicalDomain" xlink:type="arc" order="20" />
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/srt/2024/elts/srt-2024.xsd#srt_SegmentGeographicalDomain" xlink:label="loc_srtSegmentGeographicalDomain_10" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xbrldt:contextElement="segment" xlink:from="loc_srtStatementGeographicalAxis" xlink:to="loc_srtSegmentGeographicalDomain_10" xlink:type="arc" order="30" />
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_NonUsMember" xlink:label="loc_us-gaapNonUsMember_0" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srtSegmentGeographicalDomain" xlink:to="loc_us-gaapNonUsMember_0" xlink:type="arc" order="1" />
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/srt/2024/elts/srt-2024.xsd#srt_ProductOrServiceAxis" xlink:label="loc_srtProductOrServiceAxis" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaapScheduleOfRevenuesFromExternalCustomersAndLongLivedAssetsTable" xlink:to="loc_srtProductOrServiceAxis" xlink:type="arc" order="2" />
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/srt/2024/elts/srt-2024.xsd#srt_ProductsAndServicesDomain" xlink:label="loc_srtProductsAndServicesDomain" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srtProductOrServiceAxis" xlink:to="loc_srtProductsAndServicesDomain" xlink:type="arc" order="20" />
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/srt/2024/elts/srt-2024.xsd#srt_ProductsAndServicesDomain" xlink:label="loc_srtProductsAndServicesDomain_10" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xbrldt:contextElement="segment" xlink:from="loc_srtProductOrServiceAxis" xlink:to="loc_srtProductsAndServicesDomain_10" xlink:type="arc" order="30" />
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ProductMember" xlink:label="loc_us-gaapProductMember_20" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srtProductsAndServicesDomain" xlink:to="loc_us-gaapProductMember_20" xlink:type="arc" order="21" />
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_Revenues" xlink:label="loc_us-gaapRevenues_50" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapRevenuesFromExternalCustomersAndLongLivedAssetsLineItems" xlink:to="loc_us-gaapRevenues_50" xlink:type="arc" order="0" />
    </link:definitionLink>
    <link:definitionLink xlink:type="extended" xlink:role="http://nanophase.com/role/SubsequentEventDetailsNarrative" xlink:title="999072 - Disclosure - Subsequent Event (Details Narrative)">
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_SubsequentEventLineItems" xlink:label="loc_us-gaapSubsequentEventLineItems" />
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_SubsequentEventTable" xlink:label="loc_us-gaapSubsequentEventTable" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xbrldt:contextElement="segment" xlink:from="loc_us-gaapSubsequentEventLineItems" xlink:to="loc_us-gaapSubsequentEventTable" xlink:type="arc" order="10" xbrldt:closed="true" />
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_LineOfCreditFacilityAxis" xlink:label="loc_us-gaapLineOfCreditFacilityAxis" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaapSubsequentEventTable" xlink:to="loc_us-gaapLineOfCreditFacilityAxis" xlink:type="arc" order="1" />
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_LineOfCreditFacilityLenderDomain" xlink:label="loc_us-gaapLineOfCreditFacilityLenderDomain" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaapLineOfCreditFacilityAxis" xlink:to="loc_us-gaapLineOfCreditFacilityLenderDomain" xlink:type="arc" order="20" />
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_LineOfCreditFacilityLenderDomain" xlink:label="loc_us-gaapLineOfCreditFacilityLenderDomain_10" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xbrldt:contextElement="segment" xlink:from="loc_us-gaapLineOfCreditFacilityAxis" xlink:to="loc_us-gaapLineOfCreditFacilityLenderDomain_10" xlink:type="arc" order="30" />
      <link:loc xlink:type="locator" xlink:href="nanx-20241231.xsd#nanx_ARRevolverInventoryFacilityAndNewTermLoanMember" xlink:label="loc_nanxARRevolverInventoryFacilityAndNewTermLoanMember_0" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapLineOfCreditFacilityLenderDomain" xlink:to="loc_nanxARRevolverInventoryFacilityAndNewTermLoanMember_0" xlink:type="arc" order="1" />
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_SubsequentEventTypeAxis" xlink:label="loc_us-gaapSubsequentEventTypeAxis" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaapSubsequentEventTable" xlink:to="loc_us-gaapSubsequentEventTypeAxis" xlink:type="arc" order="2" />
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_SubsequentEventTypeDomain" xlink:label="loc_us-gaapSubsequentEventTypeDomain" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaapSubsequentEventTypeAxis" xlink:to="loc_us-gaapSubsequentEventTypeDomain" xlink:type="arc" order="20" />
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_SubsequentEventTypeDomain" xlink:label="loc_us-gaapSubsequentEventTypeDomain_10" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xbrldt:contextElement="segment" xlink:from="loc_us-gaapSubsequentEventTypeAxis" xlink:to="loc_us-gaapSubsequentEventTypeDomain_10" xlink:type="arc" order="30" />
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_SubsequentEventMember" xlink:label="loc_us-gaapSubsequentEventMember_10" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapSubsequentEventTypeDomain" xlink:to="loc_us-gaapSubsequentEventMember_10" xlink:type="arc" order="12" />
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_LineOfCreditFacilityExpirationDate1" xlink:label="loc_us-gaapLineOfCreditFacilityExpirationDate1_30" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapSubsequentEventLineItems" xlink:to="loc_us-gaapLineOfCreditFacilityExpirationDate1_30" xlink:type="arc" order="0" />
    </link:definitionLink>
    <link:definitionLink xlink:type="extended" xlink:role="http://xbrl.sec.gov/ecd/role/PvpExecutiveCategoriesOnly" />
    <link:definitionLink xlink:type="extended" xlink:role="http://xbrl.sec.gov/ecd/role/PvpAdjustmentsOnly" />
    <link:definitionLink xlink:type="extended" xlink:role="http://xbrl.sec.gov/ecd/role/IndividualsOnly" />
    <link:definitionLink xlink:type="extended" xlink:role="http://xbrl.sec.gov/ecd/AwardTypeOnly" />
    <link:definitionLink xlink:type="extended" xlink:role="http://xbrl.sec.gov/ecd/role/TradingArrangementsOnly" />
</link:linkbase>
