<?xml version="1.0"?>
<ownershipDocument>
    <schemaVersion>X0201</schemaVersion>

    <documentType>3</documentType><periodOfReport>2004-01-01</periodOfReport>
    <noSecuritiesOwned>0</noSecuritiesOwned>

    <issuer>
        <issuerCik>0000004281</issuerCik>
        <issuerName>ALCOA INC</issuerName>
        <issuerTradingSymbol>AA</issuerTradingSymbol></issuer><reportingOwner>
        <reportingOwnerId>
            <rptOwnerCik>0001268015</rptOwnerCik>
            <rptOwnerName>REITAN BERNT</rptOwnerName>
        </reportingOwnerId>
        <reportingOwnerAddress>
            <rptOwnerStreet1>201 ISABELLA STREET</rptOwnerStreet1>
            <rptOwnerStreet2></rptOwnerStreet2>
            <rptOwnerCity>PITTSBURGH,</rptOwnerCity>
            <rptOwnerState>PA</rptOwnerState>
            <rptOwnerZipCode>15212</rptOwnerZipCode>
            <rptOwnerStateDescription></rptOwnerStateDescription>
        </reportingOwnerAddress>
            <reportingOwnerRelationship>
<isDirector>0</isDirector><isOfficer>1</isOfficer><isTenPercentOwner>0</isTenPercentOwner><isOther>0</isOther><officerTitle>Executive Vice President     </officerTitle></reportingOwnerRelationship></reportingOwner><derivativeTable><derivativeHolding><securityTitle><value>Employee Stock Option(Right To Buy)</value></securityTitle><conversionOrExercisePrice><value>31.4687</value></conversionOrExercisePrice><exerciseDate><value>2002-01-12</value></exerciseDate><expirationDate><value>2011-01-12</value></expirationDate><underlyingSecurity><underlyingSecurityTitle><value>Common Stock</value></underlyingSecurityTitle><underlyingSecurityShares><value>11600</value></underlyingSecurityShares></underlyingSecurity><ownershipNature><directOrIndirectOwnership><value>D</value></directOrIndirectOwnership><natureOfOwnership><value/></natureOfOwnership></ownershipNature></derivativeHolding><derivativeHolding><securityTitle><value>Employee Stock Option(Right To Buy)</value></securityTitle><conversionOrExercisePrice><value>36.035</value></conversionOrExercisePrice><exerciseDate><value>2003-01-11</value></exerciseDate><expirationDate><value>2012-01-11</value></expirationDate><underlyingSecurity><underlyingSecurityTitle><value>Common Stock</value></underlyingSecurityTitle><underlyingSecurityShares><value>68400</value></underlyingSecurityShares></underlyingSecurity><ownershipNature><directOrIndirectOwnership><value>D</value></directOrIndirectOwnership><natureOfOwnership><value/></natureOfOwnership></ownershipNature></derivativeHolding><derivativeHolding><securityTitle><value>Employee Stock Option(Right To Buy)</value></securityTitle><conversionOrExercisePrice><value>22.555</value></conversionOrExercisePrice><exerciseDate><value>2004-01-10</value><footnoteId id="F1"/></exerciseDate><expirationDate><value>2013-01-10</value></expirationDate><underlyingSecurity><underlyingSecurityTitle><value>Common Stock</value></underlyingSecurityTitle><underlyingSecurityShares><value>105400</value></underlyingSecurityShares></underlyingSecurity><ownershipNature><directOrIndirectOwnership><value>D</value></directOrIndirectOwnership><natureOfOwnership><value/></natureOfOwnership></ownershipNature></derivativeHolding><derivativeHolding><securityTitle><value>Phantom Stock Units</value></securityTitle><conversionOrExercisePrice><footnoteId id="F3"/></conversionOrExercisePrice><exerciseDate><footnoteId id="F2"/></exerciseDate><expirationDate><footnoteId id="F2"/></expirationDate><underlyingSecurity><underlyingSecurityTitle><value>Common Stock</value></underlyingSecurityTitle><underlyingSecurityShares><value>2250</value></underlyingSecurityShares></underlyingSecurity><ownershipNature><directOrIndirectOwnership><value>D</value></directOrIndirectOwnership><natureOfOwnership><value/></natureOfOwnership></ownershipNature></derivativeHolding></derivativeTable><footnotes><footnote id="F1">The option vests in three equal annual installments beginning January 10, 2004.</footnote><footnote id="F2">Phantom stock units were acquired under the Alcoa Stock Acquisition Plan.  Vested units become subject to the provisions of the Alcoa Deferred Compensation Plan and are to be paid out in cash after termination of employment.</footnote><footnote id="F3">1 For 1</footnote></footnotes><remarks>&quot;No securities beneficially owned for Table 1 (Non-Derivative Securities Beneficially Owned).&quot;</remarks><ownerSignature><signatureName>Brenda Hart (Assistant Secretary), by power of attorney</signatureName><signatureDate>2004-01-12</signatureDate></ownerSignature></ownershipDocument>

