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

    <schemaVersion>X0202</schemaVersion>

    <documentType>4</documentType>

    <periodOfReport>2006-01-10</periodOfReport>

    <issuer>
        <issuerCik>0001009304</issuerCik>
        <issuerName>I2 TECHNOLOGIES INC</issuerName>
        <issuerTradingSymbol>ITWO</issuerTradingSymbol>
    </issuer>

    <reportingOwner>
        <reportingOwnerId>
            <rptOwnerCik>0001114634</rptOwnerCik>
            <rptOwnerName>AMALGAMATED GADGET LP</rptOwnerName>
        </reportingOwnerId>
        <reportingOwnerAddress>
            <rptOwnerStreet1>301 COMMERCE STREET</rptOwnerStreet1>
            <rptOwnerStreet2>SUITE 3200</rptOwnerStreet2>
            <rptOwnerCity>FORT WORTH</rptOwnerCity>
            <rptOwnerState>TX</rptOwnerState>
            <rptOwnerZipCode>76102</rptOwnerZipCode>
            <rptOwnerStateDescription></rptOwnerStateDescription>
        </reportingOwnerAddress>
        <reportingOwnerRelationship>
            <isDirector>0</isDirector>
            <isOfficer>0</isOfficer>
            <isTenPercentOwner>1</isTenPercentOwner>
            <isOther>0</isOther>
        </reportingOwnerRelationship>
    </reportingOwner>

    <reportingOwner>
        <reportingOwnerId>
            <rptOwnerCik>0001167376</rptOwnerCik>
            <rptOwnerName>SCEPTER HOLDINGS INC</rptOwnerName>
        </reportingOwnerId>
        <reportingOwnerAddress>
            <rptOwnerStreet1>301 COMMERCE STREET</rptOwnerStreet1>
            <rptOwnerStreet2>SUITE 3200</rptOwnerStreet2>
            <rptOwnerCity>FORT WORTH</rptOwnerCity>
            <rptOwnerState>TX</rptOwnerState>
            <rptOwnerZipCode>76102</rptOwnerZipCode>
            <rptOwnerStateDescription></rptOwnerStateDescription>
        </reportingOwnerAddress>
        <reportingOwnerRelationship>
            <isDirector>0</isDirector>
            <isOfficer>0</isOfficer>
            <isTenPercentOwner>1</isTenPercentOwner>
            <isOther>0</isOther>
        </reportingOwnerRelationship>
    </reportingOwner>

    <reportingOwner>
        <reportingOwnerId>
            <rptOwnerCik>0001199406</rptOwnerCik>
            <rptOwnerName>RAYNOR GEOFFREY</rptOwnerName>
        </reportingOwnerId>
        <reportingOwnerAddress>
            <rptOwnerStreet1>301 COMMERCE STREET</rptOwnerStreet1>
            <rptOwnerStreet2>SUITE 3200</rptOwnerStreet2>
            <rptOwnerCity>FORT WORTH</rptOwnerCity>
            <rptOwnerState>TX</rptOwnerState>
            <rptOwnerZipCode>76102</rptOwnerZipCode>
            <rptOwnerStateDescription></rptOwnerStateDescription>
        </reportingOwnerAddress>
        <reportingOwnerRelationship>
            <isDirector>0</isDirector>
            <isOfficer>0</isOfficer>
            <isTenPercentOwner>1</isTenPercentOwner>
            <isOther>0</isOther>
        </reportingOwnerRelationship>
    </reportingOwner>

    <derivativeTable>
        <derivativeTransaction>
            <securityTitle>
                <value>2.5% Series B Convertible Preferred Stock</value>
            </securityTitle>
            <conversionOrExercisePrice>
                <value>23.15</value>
            </conversionOrExercisePrice>
            <transactionDate>
                <value>2006-01-10</value>
            </transactionDate>
            <transactionCoding>
                <transactionFormType>4</transactionFormType>
                <transactionCode>J</transactionCode>
                <equitySwapInvolved>0</equitySwapInvolved>
                <footnoteId id="F1"/>
            </transactionCoding>
            <transactionAmounts>
                <transactionShares>
                    <value>1294</value>
                </transactionShares>
                <transactionPricePerShare>
                    <footnoteId id="F1"/>
                </transactionPricePerShare>
                <transactionAcquiredDisposedCode>
                    <value>A</value>
                </transactionAcquiredDisposedCode>
            </transactionAmounts>
            <exerciseDate>
                <footnoteId id="F2"/>
            </exerciseDate>
            <expirationDate>
                <footnoteId id="F2"/>
            </expirationDate>
            <underlyingSecurity>
                <underlyingSecurityTitle>
                    <value>Common Stock</value>
                </underlyingSecurityTitle>
                <underlyingSecurityShares>
                    <value>55896</value>
                </underlyingSecurityShares>
            </underlyingSecurity>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>103999</value>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>D</value>
                    <footnoteId id="F3"/>
                </directOrIndirectOwnership>
                <natureOfOwnership>
                    <value></value>
                </natureOfOwnership>
            </ownershipNature>
        </derivativeTransaction>
    </derivativeTable>

    <footnotes>
        <footnote id="F1">Received pursuant to a stock dividend paid on i2 Technologies, Inc.'s 2.5% Series B Convertible Preferred Stock.</footnote>
        <footnote id="F2">The Preferred Stock is immediately convertible into Common Stock at a conversion rate of 43.196544276 shares of Common Stock per share of Preferred Stock.  Unless earlier redeemed or converted, the Preferred Stock automatically converts into Common Stock on June 3, 2014.</footnote>
        <footnote id="F3">All shares reported herein as being owned by Amalgamated Gadget, L.P. (&quot;Amalgamated&quot;) were acquired by Amalgamated, for and on behalf of R2 Investments, LDC (&quot;R2&quot;), pursuant to an Investment Management Agreement. Pursuant to such Agreement, Amalgamated has sole voting and dispositive power of such shares and R2 has no beneficial ownership of such shares. This filing shall not be deemed an admission that Amalgamated is the beneficial owner of such shares for purposes of Section 16 of the Securities Exchange Act of 1934 (the &quot;Act&quot;). Scepter Holdings, Inc. (&quot;Scepter&quot;) is the general partner of Amalgamated, which is the holder of the shares reported herein. Geoffrey P. Raynor (&quot;Raynor&quot;) is the sole shareholder of Scepter. Pursuant to Rule 16a-1(a)(2)(ii)(B) under the Act, each of Scepter and Raynor is deemed to be the beneficial owner of any shares beneficially owned by Amalgamated only to the extent of the greater of his or its respective direct or indirect interest.</footnote>
    </footnotes>

    <remarks></remarks>

    <ownerSignature>
        <signatureName>Brandon Teague, Director of Trading for Scepter Holdings, Inc., general partner of Amalgamated Gadget, L.P.</signatureName>
        <signatureDate>2006-01-11</signatureDate>
    </ownerSignature>

    <ownerSignature>
        <signatureName>Brandon Teague, Director of Trading for Scepter Holdings, Inc.</signatureName>
        <signatureDate>2006-01-11</signatureDate>
    </ownerSignature>

    <ownerSignature>
        <signatureName>Geoffrey P. Raynor</signatureName>
        <signatureDate>2006-01-11</signatureDate>
    </ownerSignature>
</ownershipDocument>
