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Proc-Type: 2001,MIC-CLEAR
Originator-Name: webmaster@www.sec.gov
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MIC-Info: RSA-MD5,RSA,
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<SEC-DOCUMENT>0001127602-10-025626.txt : 20101019
<SEC-HEADER>0001127602-10-025626.hdr.sgml : 20101019
<ACCEPTANCE-DATETIME>20101019112556
ACCESSION NUMBER:		0001127602-10-025626
CONFORMED SUBMISSION TYPE:	4
PUBLIC DOCUMENT COUNT:		1
CONFORMED PERIOD OF REPORT:	20101015
FILED AS OF DATE:		20101019
DATE AS OF CHANGE:		20101019

REPORTING-OWNER:	

	OWNER DATA:	
		COMPANY CONFORMED NAME:			CORCORAN THOMAS A
		CENTRAL INDEX KEY:			0001186913

	FILING VALUES:
		FORM TYPE:		4
		SEC ACT:		1934 Act
		SEC FILE NUMBER:	001-01520
		FILM NUMBER:		101129618

	MAIL ADDRESS:	
		STREET 1:		3790 VIA DE LA VALLE
		STREET 2:		SUITE 311
		CITY:			DEL MAR
		STATE:			CA
		ZIP:			92014

ISSUER:		

	COMPANY DATA:	
		COMPANY CONFORMED NAME:			GENCORP INC
		CENTRAL INDEX KEY:			0000040888
		STANDARD INDUSTRIAL CLASSIFICATION:	FABRICATED RUBBER PRODUCTS, NEC [3060]
		IRS NUMBER:				340244000
		STATE OF INCORPORATION:			OH
		FISCAL YEAR END:			1130

	BUSINESS ADDRESS:	
		STREET 1:		HIGHWAY 50 & AEROJET ROAD
		CITY:			RANCHO CORDOVA
		STATE:			CA
		ZIP:			95670
		BUSINESS PHONE:		9163554000

	MAIL ADDRESS:	
		STREET 1:		HIGHWAY 50 & AEROJET ROAD
		CITY:			RANCHO CORDOVA
		STATE:			CA
		ZIP:			95670

	FORMER COMPANY:	
		FORMER CONFORMED NAME:	GENERAL TIRE & RUBBER CO
		DATE OF NAME CHANGE:	19840330
</SEC-HEADER>
<DOCUMENT>
<TYPE>4
<SEQUENCE>1
<FILENAME>form4.xml
<DESCRIPTION>PRIMARY DOCUMENT
<TEXT>
<XML>
<?xml version="1.0"?>
<ownershipDocument>

    <schemaVersion>X0303</schemaVersion>

    <documentType>4</documentType>

    <periodOfReport>2010-10-15</periodOfReport>

    <issuer>
        <issuerCik>0000040888</issuerCik>
        <issuerName>GENCORP INC</issuerName>
        <issuerTradingSymbol>GY</issuerTradingSymbol>
    </issuer>

    <reportingOwner>
        <reportingOwnerId>
            <rptOwnerCik>0001186913</rptOwnerCik>
            <rptOwnerName>CORCORAN THOMAS A</rptOwnerName>
        </reportingOwnerId>
        <reportingOwnerAddress>
            <rptOwnerStreet1>HIGHWAY 50 &amp; AEROJET ROAD</rptOwnerStreet1>
            <rptOwnerStreet2></rptOwnerStreet2>
            <rptOwnerCity>RANCHO CORDOVA</rptOwnerCity>
            <rptOwnerState>CA</rptOwnerState>
            <rptOwnerZipCode>95742</rptOwnerZipCode>
            <rptOwnerStateDescription></rptOwnerStateDescription>
        </reportingOwnerAddress>
        <reportingOwnerRelationship>
            <isDirector>1</isDirector>
        </reportingOwnerRelationship>
    </reportingOwner>

    <nonDerivativeTable>
        <nonDerivativeTransaction>
            <securityTitle>
                <value>Common Stock</value>
                <footnoteId id="F1"/>
            </securityTitle>
            <transactionDate>
                <value>2010-10-15</value>
            </transactionDate>
            <transactionCoding>
                <transactionFormType>4</transactionFormType>
                <transactionCode>A</transactionCode>
                <equitySwapInvolved>0</equitySwapInvolved>
            </transactionCoding>
            <transactionTimeliness></transactionTimeliness>
            <transactionAmounts>
                <transactionShares>
                    <value>1361</value>
                </transactionShares>
                <transactionPricePerShare>
                    <value>0</value>
                </transactionPricePerShare>
                <transactionAcquiredDisposedCode>
                    <value>A</value>
                </transactionAcquiredDisposedCode>
            </transactionAmounts>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>28626</value>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>D</value>
                </directOrIndirectOwnership>
            </ownershipNature>
        </nonDerivativeTransaction>
        <nonDerivativeTransaction>
            <securityTitle>
                <value>Common Stock</value>
                <footnoteId id="F2"/>
            </securityTitle>
            <transactionDate>
                <value>2010-10-15</value>
            </transactionDate>
            <transactionCoding>
                <transactionFormType>4</transactionFormType>
                <transactionCode>A</transactionCode>
                <equitySwapInvolved>0</equitySwapInvolved>
            </transactionCoding>
            <transactionTimeliness></transactionTimeliness>
            <transactionAmounts>
                <transactionShares>
                    <value>680</value>
                </transactionShares>
                <transactionPricePerShare>
                    <value>0</value>
                </transactionPricePerShare>
                <transactionAcquiredDisposedCode>
                    <value>A</value>
                </transactionAcquiredDisposedCode>
            </transactionAmounts>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>29306</value>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>D</value>
                </directOrIndirectOwnership>
            </ownershipNature>
        </nonDerivativeTransaction>
    </nonDerivativeTable>

    <footnotes>
        <footnote id="F1">Effective March 24, 2010, the Board of Directors approved a new Director Compensation Program which allows Directors to receive GenCorp common stock in lieu of their cash compensation.  The number of shares of common stock shown reflects the common stock received by this Director in lieu of his annual cash retainer fees.</footnote>
        <footnote id="F2">Pursuant to the new Director Compensation Program, if a Director elects to receive common stock in lieu of at least 50% of his cash compensation, the Company will grant restricted shares equal in value to 50% of the amount of cash compensation he elects to receive in common stock.  Such restricted shares will vest on the earlier of (i) the date of the Director's retirement from the Board, and (ii) one year after the grant date.  The number of shares of common stock shown reflects the grant of restricted shares.</footnote>
    </footnotes>

    <ownerSignature>
        <signatureName>Rebecca A. Bauer as Attorney-in-Fact</signatureName>
        <signatureDate>2010-10-19</signatureDate>
    </ownerSignature>
</ownershipDocument>
</XML>
</TEXT>
</DOCUMENT>
</SEC-DOCUMENT>
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