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Proc-Type: 2001,MIC-CLEAR
Originator-Name: webmaster@www.sec.gov
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 TWSM7vrzLADbmYQaionwg5sDW3P6oaM5D3tdezXMm7z1T+B+twIDAQAB
MIC-Info: RSA-MD5,RSA,
 CCt4RHqAYhMTSYdKKVFXRJKyKejbe+VtiV4cFJ1opRSIhY867MmWERR8sGJX5/c+
 4gysX+QDXiHH/XwHElnnfQ==

<SEC-DOCUMENT>0000091142-08-000041.txt : 20080716
<SEC-HEADER>0000091142-08-000041.hdr.sgml : 20080716
<ACCEPTANCE-DATETIME>20080716121210
ACCESSION NUMBER:		0000091142-08-000041
CONFORMED SUBMISSION TYPE:	4
PUBLIC DOCUMENT COUNT:		1
CONFORMED PERIOD OF REPORT:	20080714
FILED AS OF DATE:		20080716
DATE AS OF CHANGE:		20080716

ISSUER:		

	COMPANY DATA:	
		COMPANY CONFORMED NAME:			SMITH A O CORP
		CENTRAL INDEX KEY:			0000091142
		STANDARD INDUSTRIAL CLASSIFICATION:	MOTORS & GENERATORS [3621]
		IRS NUMBER:				390619790
		STATE OF INCORPORATION:			DE
		FISCAL YEAR END:			1231

	BUSINESS ADDRESS:	
		STREET 1:		P O BOX 245009
		CITY:			MILWAUKEE
		STATE:			WI
		ZIP:			53224-9509
		BUSINESS PHONE:		4143594000

	MAIL ADDRESS:	
		STREET 1:		P O BOX 245009
		CITY:			MILWAUKEE
		STATE:			WI
		ZIP:			53224-9509

REPORTING-OWNER:	

	OWNER DATA:	
		COMPANY CONFORMED NAME:			CURRENT GLOSTER B JR
		CENTRAL INDEX KEY:			0001399736

	FILING VALUES:
		FORM TYPE:		4
		SEC ACT:		1934 Act
		SEC FILE NUMBER:	001-00475
		FILM NUMBER:		08954576

	BUSINESS ADDRESS:	
		BUSINESS PHONE:		414-271-1444

	MAIL ADDRESS:	
		STREET 1:		NORTHWESTERN MUTUAL LIFE INSURANCE CO.
		STREET 2:		720 E. WISCONSIN AVE.
		CITY:			MILWAUKEE
		STATE:			WI
		ZIP:			53202
</SEC-HEADER>
<DOCUMENT>
<TYPE>4
<SEQUENCE>1
<FILENAME>edgar.xml
<DESCRIPTION>PRIMARY DOCUMENT
<TEXT>
<XML>
<?xml version="1.0"?>
<ownershipDocument>

    <schemaVersion>X0303</schemaVersion>

    <documentType>4</documentType>

    <periodOfReport>2008-07-14</periodOfReport>

    <issuer>
        <issuerCik>0000091142</issuerCik>
        <issuerName>SMITH A O CORP</issuerName>
        <issuerTradingSymbol>AOS</issuerTradingSymbol>
    </issuer>

    <reportingOwner>
        <reportingOwnerId>
            <rptOwnerCik>0001399736</rptOwnerCik>
            <rptOwnerName>CURRENT GLOSTER B JR</rptOwnerName>
        </reportingOwnerId>
        <reportingOwnerAddress>
            <rptOwnerStreet1>NORTHWESTERN MUTUAL LIFE INSURANCE CO.</rptOwnerStreet1>
            <rptOwnerStreet2>720 EAST WISCONSIN AVENUE</rptOwnerStreet2>
            <rptOwnerCity>MILWAUKEE</rptOwnerCity>
            <rptOwnerState>WI</rptOwnerState>
            <rptOwnerZipCode>53202</rptOwnerZipCode>
            <rptOwnerStateDescription></rptOwnerStateDescription>
        </reportingOwnerAddress>
        <reportingOwnerRelationship>
            <isDirector>1</isDirector>
            <isOfficer>0</isOfficer>
            <isTenPercentOwner>0</isTenPercentOwner>
            <isOther>0</isOther>
        </reportingOwnerRelationship>
    </reportingOwner>

    <nonDerivativeTable>
        <nonDerivativeTransaction>
            <securityTitle>
                <value>Common Stock</value>
            </securityTitle>
            <transactionDate>
                <value>2008-07-14</value>
            </transactionDate>
            <transactionCoding>
                <transactionFormType>4</transactionFormType>
                <transactionCode>A</transactionCode>
                <equitySwapInvolved>0</equitySwapInvolved>
            </transactionCoding>
            <transactionAmounts>
                <transactionShares>
                    <value>680</value>
                    <footnoteId id="F1"/>
                </transactionShares>
                <transactionPricePerShare>
                    <value>33.12</value>
                </transactionPricePerShare>
                <transactionAcquiredDisposedCode>
                    <value>A</value>
                </transactionAcquiredDisposedCode>
            </transactionAmounts>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>4687</value>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>D</value>
                </directOrIndirectOwnership>
                <natureOfOwnership>
                    <value></value>
                </natureOfOwnership>
            </ownershipNature>
        </nonDerivativeTransaction>
    </nonDerivativeTable>

    <footnotes>
        <footnote id="F1">Payment of portion of retainer in stock under the A. O. Smith Corporation Directors' Compensation Plan based on the market price of the Common Stock on July 14, 2008.</footnote>
    </footnotes>

    <remarks></remarks>

    <ownerSignature>
        <signatureName>James F. Stern, Attorney-in-Fact for Gloster B. Current, Jr.</signatureName>
        <signatureDate>2008-07-16</signatureDate>
    </ownerSignature>
</ownershipDocument>
</XML>
</TEXT>
</DOCUMENT>
</SEC-DOCUMENT>
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