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

    <documentType>4/A</documentType><periodOfReport>2003-08-31</periodOfReport><dateOfOriginalSubmission>2003-08-31</dateOfOriginalSubmission>
    <issuer>
        <issuerCik>0001008554</issuerCik>
        <issuerName>HUMBOLDT BANCORP</issuerName>
        <issuerTradingSymbol>HBEK</issuerTradingSymbol></issuer><reportingOwner>
        <reportingOwnerId>
            <rptOwnerCik>0001102044</rptOwnerCik>
            <rptOwnerName>WINZLER JOHN R</rptOwnerName>
        </reportingOwnerId>
        <reportingOwnerAddress>
            <rptOwnerStreet1>C/O HUMBOLDT BANCORP</rptOwnerStreet1>
            <rptOwnerStreet2>2998 DOUGLAS BLVD., SUITE 330</rptOwnerStreet2>
            <rptOwnerCity>ROSEVILLE</rptOwnerCity>
            <rptOwnerState>CA</rptOwnerState>
            <rptOwnerZipCode>95661</rptOwnerZipCode>
            <rptOwnerStateDescription></rptOwnerStateDescription>
        </reportingOwnerAddress>
            <reportingOwnerRelationship>
<isDirector>1</isDirector><isOfficer>0</isOfficer><isTenPercentOwner>0</isTenPercentOwner><isOther>0</isOther></reportingOwnerRelationship></reportingOwner><derivativeTable><derivativeTransaction><securityTitle><value>Deferred Rights</value></securityTitle><conversionOrExercisePrice><value>0</value><footnoteId id="F1"/></conversionOrExercisePrice><transactionDate><value>2003-08-31</value></transactionDate><transactionCoding><transactionFormType>4</transactionFormType><transactionCode>A</transactionCode><equitySwapInvolved>0</equitySwapInvolved></transactionCoding><transactionAmounts><transactionShares><value>319</value><footnoteId id="F2"/></transactionShares><transactionPricePerShare><value>14.889</value></transactionPricePerShare><transactionAcquiredDisposedCode><value>A</value></transactionAcquiredDisposedCode></transactionAmounts><exerciseDate><value>1988-08-08</value><footnoteId id="F1"/></exerciseDate><expirationDate><value>1988-08-08</value><footnoteId id="F1"/></expirationDate><underlyingSecurity><underlyingSecurityTitle><value>Common Stock </value><footnoteId id="F1"/></underlyingSecurityTitle><underlyingSecurityShares><value>319</value><footnoteId id="F2"/></underlyingSecurityShares></underlyingSecurity><postTransactionAmounts><sharesOwnedFollowingTransaction><value>19152</value><footnoteId id="F3"/></sharesOwnedFollowingTransaction></postTransactionAmounts><ownershipNature><directOrIndirectOwnership><value>D</value></directOrIndirectOwnership><natureOfOwnership><value/></natureOfOwnership></ownershipNature></derivativeTransaction></derivativeTable><footnotes><footnote id="F1">Represents the reporting person's director's fee under Humboldt Bancorp's deferred compensation plan. Under the plan, the director has the right to defer their director's fee to be paid in common stock upon resignation or retirement. The conversion price of the derivative security is 1 for 1, the number of shares purchased for the month are based on the closing price on the last trade date of the month for which the director fees are paid. </footnote><footnote id="F2">Director Fee was not properly recorded, should have been $4,750 vs. $1,800. Changes the amount of shares deferred by 319 vs. 121 previously reported. </footnote><footnote id="F3">Director Fee was not properly recorded, should have been $4,750 vs. $1,800. Changes the amount of shares deferred by 319 vs. 121 previously reported. The total Beneficial Ownership is adjusted for the miscalculation of 198 deferred shares.</footnote></footnotes><remarks/><ownerSignature><signatureName>John R. Winzler</signatureName><signatureDate>2003-11-03</signatureDate></ownerSignature><ownerSignature><signatureName>Signed by Patrick J. Rusnak, Power of Attorney on File </signatureName><signatureDate>2003-11-03</signatureDate></ownerSignature></ownershipDocument>

