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Proc-Type: 2001,MIC-CLEAR
Originator-Name: webmaster@www.sec.gov
Originator-Key-Asymmetric:
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 TWSM7vrzLADbmYQaionwg5sDW3P6oaM5D3tdezXMm7z1T+B+twIDAQAB
MIC-Info: RSA-MD5,RSA,
 J7N7cu23FEvKlHsi8FWCfw76PCLDyIaeKey7hgNZotmLLAOYHns6MIZk7Z6dyRZP
 I0NwDaAmSP0ewQYJdvP7+Q==

<SEC-DOCUMENT>0001250608-08-000008.txt : 20080623
<SEC-HEADER>0001250608-08-000008.hdr.sgml : 20080623
<ACCEPTANCE-DATETIME>20080623165932
ACCESSION NUMBER:		0001250608-08-000008
CONFORMED SUBMISSION TYPE:	4
PUBLIC DOCUMENT COUNT:		1
CONFORMED PERIOD OF REPORT:	20080619
FILED AS OF DATE:		20080623
DATE AS OF CHANGE:		20080623

ISSUER:		

	COMPANY DATA:	
		COMPANY CONFORMED NAME:			MENTOR GRAPHICS CORP
		CENTRAL INDEX KEY:			0000701811
		STANDARD INDUSTRIAL CLASSIFICATION:	SERVICES-COMPUTER INTEGRATED SYSTEMS DESIGN [7373]
		IRS NUMBER:				930786033
		STATE OF INCORPORATION:			OR
		FISCAL YEAR END:			0131

	BUSINESS ADDRESS:	
		STREET 1:		8005 SW BOECKMAN RD
		CITY:			WILSONVILLE
		STATE:			OR
		ZIP:			97070-7777
		BUSINESS PHONE:		5036857000

REPORTING-OWNER:	

	OWNER DATA:	
		COMPANY CONFORMED NAME:			BONFIELD PETER L
		CENTRAL INDEX KEY:			0001239173

	FILING VALUES:
		FORM TYPE:		4
		SEC ACT:		1934 Act
		SEC FILE NUMBER:	000-13442
		FILM NUMBER:		08912602

	MAIL ADDRESS:	
		STREET 1:		C/OMENTOR GRAPHICS CORP
		STREET 2:		8005 SW BOECKMAN ROAD
		CITY:			WILSONVILLE
		STATE:			OR
		ZIP:			97070-7777
</SEC-HEADER>
<DOCUMENT>
<TYPE>4
<SEQUENCE>1
<FILENAME>primary_doc.xml
<DESCRIPTION>PRIMARY DOCUMENT
<TEXT>
<XML>
<?xml version="1.0"?>
<ownershipDocument>

    <schemaVersion>X0303</schemaVersion>

    <documentType>4</documentType>

    <periodOfReport>2008-06-19</periodOfReport>

    <notSubjectToSection16>0</notSubjectToSection16>

    <issuer>
        <issuerCik>0000701811</issuerCik>
        <issuerName>MENTOR GRAPHICS CORP</issuerName>
        <issuerTradingSymbol>MENT</issuerTradingSymbol>
    </issuer>

    <reportingOwner>
        <reportingOwnerId>
            <rptOwnerCik>0001239173</rptOwnerCik>
            <rptOwnerName>BONFIELD PETER L</rptOwnerName>
        </reportingOwnerId>
        <reportingOwnerAddress>
            <rptOwnerStreet1>C/O  MENTOR GRAPHICS CORP</rptOwnerStreet1>
            <rptOwnerStreet2>8005 SW BOECKMAN ROAD</rptOwnerStreet2>
            <rptOwnerCity>WILSONVILLE</rptOwnerCity>
            <rptOwnerState>OR</rptOwnerState>
            <rptOwnerZipCode>97070-7777</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>2008-06-19</value>
            </transactionDate>
            <transactionCoding>
                <transactionFormType>4</transactionFormType>
                <transactionCode>A</transactionCode>
                <equitySwapInvolved>0</equitySwapInvolved>
            </transactionCoding>
            <transactionTimeliness>
                <value></value>
            </transactionTimeliness>
            <transactionAmounts>
                <transactionShares>
                    <value>7000</value>
                </transactionShares>
                <transactionPricePerShare>
                    <value>0</value>
                </transactionPricePerShare>
                <transactionAcquiredDisposedCode>
                    <value>A</value>
                </transactionAcquiredDisposedCode>
            </transactionAmounts>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>14000</value>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>D</value>
                </directOrIndirectOwnership>
            </ownershipNature>
        </nonDerivativeTransaction>
    </nonDerivativeTable>

    <ownerSignature>
        <signatureName>Dean Freed, Attorney-in-fact for Peter L Bonfield</signatureName>
        <signatureDate>2008-06-23</signatureDate>
    </ownerSignature>
</ownershipDocument>
</XML>
</TEXT>
</DOCUMENT>
</SEC-DOCUMENT>
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