<?xml version="1.0"?>
<ownershipDocument>

    <schemaVersion>X0202</schemaVersion>

    <documentType>4</documentType>

    <periodOfReport>2006-01-02</periodOfReport>

    <issuer>
        <issuerCik>0000097216</issuerCik>
        <issuerName>TEREX CORP</issuerName>
        <issuerTradingSymbol>TEX</issuerTradingSymbol>
    </issuer>

    <reportingOwner>
        <reportingOwnerId>
            <rptOwnerCik>0001107623</rptOwnerCik>
            <rptOwnerName>ANDERSEN G CHRIS</rptOwnerName>
        </reportingOwnerId>
        <reportingOwnerAddress>
            <rptOwnerStreet1>C/O TEREX CORPORATION</rptOwnerStreet1>
            <rptOwnerStreet2>500 POST ROAD EAST, SUITE 320</rptOwnerStreet2>
            <rptOwnerCity>WESPORT</rptOwnerCity>
            <rptOwnerState>CT</rptOwnerState>
            <rptOwnerZipCode>06880</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, par value $.01</value>
            </securityTitle>
            <transactionDate>
                <value>2006-01-03</value>
            </transactionDate>
            <transactionCoding>
                <transactionFormType>4</transactionFormType>
                <transactionCode>P</transactionCode>
                <equitySwapInvolved>0</equitySwapInvolved>
            </transactionCoding>
            <transactionAmounts>
                <transactionShares>
                    <value>42</value>
                    <footnoteId id="F1"/>
                </transactionShares>
                <transactionPricePerShare>
                    <value>59.40</value>
                </transactionPricePerShare>
                <transactionAcquiredDisposedCode>
                    <value>A</value>
                </transactionAcquiredDisposedCode>
            </transactionAmounts>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>121667</value>
                    <footnoteId id="F2"/>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>D</value>
                </directOrIndirectOwnership>
                <natureOfOwnership>
                    <value></value>
                </natureOfOwnership>
            </ownershipNature>
        </nonDerivativeTransaction>
        <nonDerivativeTransaction>
            <securityTitle>
                <value>Common Stock, par value $.01</value>
            </securityTitle>
            <transactionDate>
                <value>2006-01-04</value>
            </transactionDate>
            <transactionCoding>
                <transactionFormType>4</transactionFormType>
                <transactionCode>P</transactionCode>
                <equitySwapInvolved>0</equitySwapInvolved>
            </transactionCoding>
            <transactionAmounts>
                <transactionShares>
                    <value>1438</value>
                    <footnoteId id="F3"/>
                </transactionShares>
                <transactionPricePerShare>
                    <value>60.84</value>
                </transactionPricePerShare>
                <transactionAcquiredDisposedCode>
                    <value>A</value>
                </transactionAcquiredDisposedCode>
            </transactionAmounts>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>123105</value>
                    <footnoteId id="F4"/>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>D</value>
                </directOrIndirectOwnership>
                <natureOfOwnership>
                    <value></value>
                </natureOfOwnership>
            </ownershipNature>
        </nonDerivativeTransaction>
    </nonDerivativeTable>

    <derivativeTable>
        <derivativeTransaction>
            <securityTitle>
                <value>Employee Stock Option (right to buy)</value>
                <footnoteId id="F5"/>
            </securityTitle>
            <conversionOrExercisePrice>
                <value>15.625</value>
            </conversionOrExercisePrice>
            <transactionDate>
                <value>2006-01-02</value>
            </transactionDate>
            <transactionCoding>
                <transactionFormType>4</transactionFormType>
                <transactionCode>A</transactionCode>
                <equitySwapInvolved>0</equitySwapInvolved>
            </transactionCoding>
            <transactionAmounts>
                <transactionShares>
                    <value>7500</value>
                </transactionShares>
                <transactionPricePerShare>
                    <value>0</value>
                </transactionPricePerShare>
                <transactionAcquiredDisposedCode>
                    <value>A</value>
                </transactionAcquiredDisposedCode>
            </transactionAmounts>
            <exerciseDate>
                <value>2001-01-02</value>
            </exerciseDate>
            <expirationDate>
                <footnoteId id="F6"/>
            </expirationDate>
            <underlyingSecurity>
                <underlyingSecurityTitle>
                    <value>Common Stock, par value $.01</value>
                </underlyingSecurityTitle>
                <underlyingSecurityShares>
                    <value>7500</value>
                </underlyingSecurityShares>
            </underlyingSecurity>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>7500</value>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>D</value>
                </directOrIndirectOwnership>
                <natureOfOwnership>
                    <value></value>
                </natureOfOwnership>
            </ownershipNature>
        </derivativeTransaction>
    </derivativeTable>

    <footnotes>
        <footnote id="F1">Shares purchased through Company Deferred Compensation Plan representing payment of fourth quarter meeting fees.</footnote>
        <footnote id="F2">Represents shares beneficially owned as of January 3, 2006.</footnote>
        <footnote id="F3">Shares purchased through Company Deferred Compensation Plan representing payment of annual director retainer and committee retainer fees.</footnote>
        <footnote id="F4">Represents shares beneficially owned as of January 4, 2006.</footnote>
        <footnote id="F5">Stock option granted on January 2, 2001, pursuant to one of the Company's long-term incentive plans, with a five year term.</footnote>
        <footnote id="F6">As a result of the Company's previously disclosed restatement process, the Company determined that all Terex employees, former employees and directors are unable to exercise any options to purchase Terex common stock until completion of the restatement process.  Accordingly, the Company's Board of Directors has determined that the Company will honor any options to purchase shares of the Company's common stock that have been granted pursuant to any of the Company's long-term incentive plans, which options otherwise would have expired unexercised solely because the individuals owning such options are currently unable to exercise such options prior to their expiration due to the Company's restatement process.  This limited accommodation will be for a period of thirty (30) days from the date that the Company determines that it is first permissible to exercise such options.</footnote>
    </footnotes>

    <remarks></remarks>

    <ownerSignature>
        <signatureName>/s/ G. Chris Andersen</signatureName>
        <signatureDate>2006-01-04</signatureDate>
    </ownerSignature>
</ownershipDocument>
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X0202
4
2006-01-02
0000097216
TEREX CORP
TEX
0001107623
ANDERSEN G CHRIS
C/O TEREX CORPORATION
500 POST ROAD EAST, SUITE 320
WESPORT
CT
06880
1
0
0
0
Common Stock, par value $.01
2006-01-03
4
P
0
42
59.40
A
121667
D
Common Stock, par value $.01
2006-01-04
4
P
0
1438
60.84
A
123105
D
Employee Stock Option (right to buy)
15.625
2006-01-02
4
A
0
7500
0
A
2001-01-02
Common Stock, par value $.01
7500
7500
D
Shares purchased through Company Deferred Compensation Plan representing payment of fourth quarter meeting fees.
Represents shares beneficially owned as of January 3, 2006.
Shares purchased through Company Deferred Compensation Plan representing payment of annual director retainer and committee retainer fees.
Represents shares beneficially owned as of January 4, 2006.
Stock option granted on January 2, 2001, pursuant to one of the Company's long-term incentive plans, with a five year term.
As a result of the Company's previously disclosed restatement process, the Company determined that all Terex employees, former employees and directors are unable to exercise any options to purchase Terex common stock until completion of the restatement process.  Accordingly, the Company's Board of Directors has determined that the Company will honor any options to purchase shares of the Company's common stock that have been granted pursuant to any of the Company's long-term incentive plans, which options otherwise would have expired unexercised solely because the individuals owning such options are currently unable to exercise such options prior to their expiration due to the Company's restatement process.  This limited accommodation will be for a period of thirty (30) days from the date that the Company determines that it is first permissible to exercise such options.
/s/ G. Chris Andersen
2006-01-04