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

    <schemaVersion>X0303</schemaVersion>

    <documentType>4</documentType>

    <periodOfReport>2010-06-11</periodOfReport>

    <notSubjectToSection16>0</notSubjectToSection16>

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

    <reportingOwner>
        <reportingOwnerId>
            <rptOwnerCik>0000905874</rptOwnerCik>
            <rptOwnerName>LANGONE KENNETH G</rptOwnerName>
        </reportingOwnerId>
        <reportingOwnerAddress>
            <rptOwnerStreet1>375 PARK AVENUE</rptOwnerStreet1>
            <rptOwnerStreet2>STE 2205</rptOwnerStreet2>
            <rptOwnerCity>NEW YORK</rptOwnerCity>
            <rptOwnerState>NY</rptOwnerState>
            <rptOwnerZipCode>10152</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</value>
            </securityTitle>
            <transactionDate>
                <value>2010-06-11</value>
            </transactionDate>
            <transactionCoding>
                <transactionFormType>4</transactionFormType>
                <transactionCode>P</transactionCode>
                <equitySwapInvolved>0</equitySwapInvolved>
            </transactionCoding>
            <transactionTimeliness>
                <value></value>
            </transactionTimeliness>
            <transactionAmounts>
                <transactionShares>
                    <value>15400</value>
                </transactionShares>
                <transactionPricePerShare>
                    <value>3.94</value>
                    <footnoteId id="F1"/>
                </transactionPricePerShare>
                <transactionAcquiredDisposedCode>
                    <value>A</value>
                </transactionAcquiredDisposedCode>
            </transactionAmounts>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>1857200</value>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>D</value>
                </directOrIndirectOwnership>
            </ownershipNature>
        </nonDerivativeTransaction>
        <nonDerivativeTransaction>
            <securityTitle>
                <value>COMMON STOCK</value>
            </securityTitle>
            <transactionDate>
                <value>2010-06-14</value>
            </transactionDate>
            <transactionCoding>
                <transactionFormType>4</transactionFormType>
                <transactionCode>P</transactionCode>
                <equitySwapInvolved>0</equitySwapInvolved>
            </transactionCoding>
            <transactionTimeliness>
                <value></value>
            </transactionTimeliness>
            <transactionAmounts>
                <transactionShares>
                    <value>18700</value>
                </transactionShares>
                <transactionPricePerShare>
                    <value>3.75</value>
                    <footnoteId id="F2"/>
                </transactionPricePerShare>
                <transactionAcquiredDisposedCode>
                    <value>A</value>
                </transactionAcquiredDisposedCode>
            </transactionAmounts>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>1875900</value>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>D</value>
                </directOrIndirectOwnership>
            </ownershipNature>
        </nonDerivativeTransaction>
        <nonDerivativeHolding>
            <securityTitle>
                <value>COMMON STOCK</value>
            </securityTitle>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>270000</value>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>I</value>
                </directOrIndirectOwnership>
                <natureOfOwnership>
                    <value>by Invemed Associates LLC</value>
                    <footnoteId id="F3"/>
                </natureOfOwnership>
            </ownershipNature>
        </nonDerivativeHolding>
    </nonDerivativeTable>

    <footnotes>
        <footnote id="F1">The Reporting Person executed a trade order through a broker-dealer which resulted in multiple same-day same-way open market purchases, with the prices ranging from $3.80 to $4.00/share.  The Reporting Person has reported these purchases on an aggregate basis using the weighted average price for the transactions and will provide detailed breakouts upon request.</footnote>
        <footnote id="F2">The Reporting Person executed a trade order through a broker-dealer which resulted in multiple same-day same-way open market purchases, with the prices ranging from $3.69 to $3.77/share.  The Reporting Person has reported these purchases on an aggregate basis using the weighted average price for the transactions and will provide detailed breakouts upon request.</footnote>
        <footnote id="F3">The Reporting Person is the principal equityholder and President and CEO of Invemed Associates, LLC.  Pursuant to Instruction (4)(b)(iv) of Form 4, the Reporting Person has elected to reprot as indirectly beneficially owned the entire number of securities beneficially owned by such entity.  The Reporting Person disclaims beneficial ownership of any securities, and any proceeds thereof, that exceed his pecuniary interest therein and/or that are not actually distributed to him.</footnote>
    </footnotes>

    <ownerSignature>
        <signatureName>/s/Kenneth G. Langone/Charles F. McCoy, POA</signatureName>
        <signatureDate>2010-06-14</signatureDate>
    </ownerSignature>
</ownershipDocument>
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X0303
4
2010-06-11
0
0000100726
UNIFI INC
UFI
0000905874
LANGONE KENNETH G
375 PARK AVENUE
STE 2205
NEW YORK
NY
10152
1
0
0
0
COMMON STOCK
2010-06-11
4
P
0
15400
3.94
A
1857200
D
COMMON STOCK
2010-06-14
4
P
0
18700
3.75
A
1875900
D
COMMON STOCK
270000
I
by Invemed Associates LLC
The Reporting Person executed a trade order through a broker-dealer which resulted in multiple same-day same-way open market purchases, with the prices ranging from $3.80 to $4.00/share.  The Reporting Person has reported these purchases on an aggregate basis using the weighted average price for the transactions and will provide detailed breakouts upon request.
The Reporting Person executed a trade order through a broker-dealer which resulted in multiple same-day same-way open market purchases, with the prices ranging from $3.69 to $3.77/share.  The Reporting Person has reported these purchases on an aggregate basis using the weighted average price for the transactions and will provide detailed breakouts upon request.
The Reporting Person is the principal equityholder and President and CEO of Invemed Associates, LLC.  Pursuant to Instruction (4)(b)(iv) of Form 4, the Reporting Person has elected to reprot as indirectly beneficially owned the entire number of securities beneficially owned by such entity.  The Reporting Person disclaims beneficial ownership of any securities, and any proceeds thereof, that exceed his pecuniary interest therein and/or that are not actually distributed to him.
/s/Kenneth G. Langone/Charles F. McCoy, POA
2010-06-14