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Proc-Type: 2001,MIC-CLEAR
Originator-Name: webmaster@www.sec.gov
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MIC-Info: RSA-MD5,RSA,
 B34geXxiFO+NTupXMAaLLsnOlBYvS1T22YmC0CMbpxHNiP4C4KQWbzlF+/54K2zf
 OCjdSNhftgDUCBtWEzTUOw==

<SEC-DOCUMENT>0001020062-05-000007.txt : 20050203
<SEC-HEADER>0001020062-05-000007.hdr.sgml : 20050203
<ACCEPTANCE-DATETIME>20050203183027
ACCESSION NUMBER:		0001020062-05-000007
CONFORMED SUBMISSION TYPE:	5
PUBLIC DOCUMENT COUNT:		1
CONFORMED PERIOD OF REPORT:	20041231
FILED AS OF DATE:		20050203
DATE AS OF CHANGE:		20050203

ISSUER:		

	COMPANY DATA:	
		COMPANY CONFORMED NAME:			GATX CORP
		CENTRAL INDEX KEY:			0000040211
		STANDARD INDUSTRIAL CLASSIFICATION:	TRANSPORTATION SERVICES [4700]
		IRS NUMBER:				361124040
		STATE OF INCORPORATION:			NY
		FISCAL YEAR END:			1231

	BUSINESS ADDRESS:	
		STREET 1:		500 W MONROE ST
		CITY:			CHICAGO
		STATE:			IL
		ZIP:			60661
		BUSINESS PHONE:		3126216200

	FORMER COMPANY:	
		FORMER CONFORMED NAME:	GENERAL AMERICAN TRANSPORTATION CORP
		DATE OF NAME CHANGE:	19750722

REPORTING-OWNER:	

	OWNER DATA:	
		COMPANY CONFORMED NAME:			FRETZ DEBORAH M
		CENTRAL INDEX KEY:			0001020062

	FILING VALUES:
		FORM TYPE:		5
		SEC ACT:		1934 Act
		SEC FILE NUMBER:	001-02328
		FILM NUMBER:		05574696

	BUSINESS ADDRESS:	
		BUSINESS PHONE:		2159773197

	MAIL ADDRESS:	
		STREET 1:		1801 MARKET STREET
		CITY:			PHILADELPHIA
		STATE:			PA
		ZIP:			19103
</SEC-HEADER>
<DOCUMENT>
<TYPE>5
<SEQUENCE>1
<FILENAME>doc5.xml
<DESCRIPTION>PRIMARY DOCUMENT
<TEXT>
<XML>
<?xml version="1.0"?>
<ownershipDocument>

    <schemaVersion>X0202</schemaVersion>

    <documentType>5</documentType>

    <periodOfReport>2004-12-31</periodOfReport>

    <notSubjectToSection16>0</notSubjectToSection16>

    <form3HoldingsReported>0</form3HoldingsReported>

    <form4TransactionsReported>0</form4TransactionsReported>

    <issuer>
        <issuerCik>0000040211</issuerCik>
        <issuerName>GATX CORP</issuerName>
        <issuerTradingSymbol>GMT</issuerTradingSymbol>
    </issuer>

    <reportingOwner>
        <reportingOwnerId>
            <rptOwnerCik>0001020062</rptOwnerCik>
            <rptOwnerName>FRETZ DEBORAH M</rptOwnerName>
        </reportingOwnerId>
        <reportingOwnerAddress>
            <rptOwnerStreet1>SUNOCO LOGISTICS PARTNERS L.P.</rptOwnerStreet1>
            <rptOwnerStreet2>1801 MARKET STREET</rptOwnerStreet2>
            <rptOwnerCity>PHILADELPHIA</rptOwnerCity>
            <rptOwnerState>PA</rptOwnerState>
            <rptOwnerZipCode>19103-1699</rptOwnerZipCode>
            <rptOwnerStateDescription></rptOwnerStateDescription>
        </reportingOwnerAddress>
        <reportingOwnerRelationship>
            <isDirector>1</isDirector>
            <isOfficer>0</isOfficer>
            <isTenPercentOwner>0</isTenPercentOwner>
            <isOther>0</isOther>
        </reportingOwnerRelationship>
    </reportingOwner>

    <nonDerivativeTable>
        <nonDerivativeHolding>
            <securityTitle>
                <value>Common Stock</value>
                <footnoteId id="F1"/>
            </securityTitle>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>12783.76</value>
                    <footnoteId id="F1"/>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>D</value>
                </directOrIndirectOwnership>
            </ownershipNature>
        </nonDerivativeHolding>
    </nonDerivativeTable>

    <derivativeTable></derivativeTable>

    <footnotes>
        <footnote id="F1">This amount reflects shares purchased through the dividend reinvestment plan, in the amount of .0395 shares, which is the reivestment of dividends from the one commemorative gift share given by the company in honor of GATX Corporation's centennial.</footnote>
    </footnotes>

    <remarks></remarks>

    <ownerSignature>
        <signatureName>Lisa M. Ibarra, by Power of Attorney on behalf of Deborah M.</signatureName>
        <signatureDate>2005-02-01</signatureDate>
    </ownerSignature>
</ownershipDocument>

</XML>
</TEXT>
</DOCUMENT>
</SEC-DOCUMENT>
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