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

    <schemaVersion>X0202</schemaVersion>

    <documentType>4</documentType>

    <periodOfReport>2007-10-24</periodOfReport>

    <notSubjectToSection16>0</notSubjectToSection16>

    <issuer>
        <issuerCik>0000100726</issuerCik>
        <issuerName>UNIFI INC</issuerName>
        <issuerTradingSymbol>UFI</issuerTradingSymbol>
    </issuer>

    <reportingOwner>
        <reportingOwnerId>
            <rptOwnerCik>0001289858</rptOwnerCik>
            <rptOwnerName>McCoy Charles Floyd</rptOwnerName>
        </reportingOwnerId>
        <reportingOwnerAddress>
            <rptOwnerStreet1>5938 TARLETON DRIVE</rptOwnerStreet1>
            <rptOwnerStreet2></rptOwnerStreet2>
            <rptOwnerCity>OAK RIDGE</rptOwnerCity>
            <rptOwnerState>NC</rptOwnerState>
            <rptOwnerZipCode>27310</rptOwnerZipCode>
            <rptOwnerStateDescription></rptOwnerStateDescription>
        </reportingOwnerAddress>
        <reportingOwnerRelationship>
            <isDirector>0</isDirector>
            <isOfficer>1</isOfficer>
            <isTenPercentOwner>0</isTenPercentOwner>
            <isOther>0</isOther>
            <officerTitle>Vice Pres, Sec &amp; Gen Counsel</officerTitle>
        </reportingOwnerRelationship>
    </reportingOwner>

    <derivativeTable>
        <derivativeTransaction>
            <securityTitle>
                <value>Stock Options (Right to Buy)</value>
            </securityTitle>
            <conversionOrExercisePrice>
                <value>2.72</value>
            </conversionOrExercisePrice>
            <transactionDate>
                <value>2007-10-24</value>
            </transactionDate>
            <transactionCoding>
                <transactionFormType>4</transactionFormType>
                <transactionCode>A</transactionCode>
                <equitySwapInvolved>0</equitySwapInvolved>
            </transactionCoding>
            <transactionTimeliness>
                <value></value>
            </transactionTimeliness>
            <transactionAmounts>
                <transactionShares>
                    <value>50000</value>
                </transactionShares>
                <transactionPricePerShare>
                    <value>0</value>
                </transactionPricePerShare>
                <transactionAcquiredDisposedCode>
                    <value>A</value>
                </transactionAcquiredDisposedCode>
            </transactionAmounts>
            <exerciseDate>
                <footnoteId id="F1"/>
            </exerciseDate>
            <expirationDate>
                <value>2017-10-24</value>
            </expirationDate>
            <underlyingSecurity>
                <underlyingSecurityTitle>
                    <value>Common Stock</value>
                </underlyingSecurityTitle>
                <underlyingSecurityShares>
                    <value>50000</value>
                </underlyingSecurityShares>
            </underlyingSecurity>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>50000</value>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>D</value>
                </directOrIndirectOwnership>
            </ownershipNature>
        </derivativeTransaction>
    </derivativeTable>

    <footnotes>
        <footnote id="F1">The Option granted shall vest and become exercisable on the date that the closing price of the Registrant's common stock on the New York Stock Exchange shall have been at least $6.00 per share for thirty (30) consecutive trading days.</footnote>
    </footnotes>

    <ownerSignature>
        <signatureName>/s/Charles F. McCoy</signatureName>
        <signatureDate>2007-10-25</signatureDate>
    </ownerSignature>
</ownershipDocument>
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X0202
4
2007-10-24
0
0000100726
UNIFI INC
UFI
0001289858
McCoy Charles Floyd
5938 TARLETON DRIVE
OAK RIDGE
NC
27310
0
1
0
0
Vice Pres, Sec & Gen Counsel
Stock Options (Right to Buy)
2.72
2007-10-24
4
A
0
50000
0
A
2017-10-24
Common Stock
50000
50000
D
The Option granted shall vest and become exercisable on the date that the closing price of the Registrant's common stock on the New York Stock Exchange shall have been at least $6.00 per share for thirty (30) consecutive trading days.
/s/Charles F. McCoy
2007-10-25