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

    <schemaVersion>X0306</schemaVersion>

    <documentType>4</documentType>

    <periodOfReport>2017-09-29</periodOfReport>

    <notSubjectToSection16>1</notSubjectToSection16>

    <issuer>
        <issuerCik>0000799729</issuerCik>
        <issuerName>PAREXEL INTERNATIONAL CORP</issuerName>
        <issuerTradingSymbol>PRXL</issuerTradingSymbol>
    </issuer>

    <reportingOwner>
        <reportingOwnerId>
            <rptOwnerCik>0001278042</rptOwnerCik>
            <rptOwnerName>GOLDBERG MARK A</rptOwnerName>
        </reportingOwnerId>
        <reportingOwnerAddress>
            <rptOwnerStreet1>C/O PAREXEL INTERNATIONAL CORPORATION</rptOwnerStreet1>
            <rptOwnerStreet2>195 WEST STREET</rptOwnerStreet2>
            <rptOwnerCity>WALTHAM</rptOwnerCity>
            <rptOwnerState>MA</rptOwnerState>
            <rptOwnerZipCode>02451</rptOwnerZipCode>
            <rptOwnerStateDescription></rptOwnerStateDescription>
        </reportingOwnerAddress>
        <reportingOwnerRelationship>
            <isDirector>0</isDirector>
            <isOfficer>1</isOfficer>
            <isTenPercentOwner>0</isTenPercentOwner>
            <isOther>0</isOther>
            <officerTitle>President &amp; COO</officerTitle>
        </reportingOwnerRelationship>
    </reportingOwner>

    <nonDerivativeTable>
        <nonDerivativeTransaction>
            <securityTitle>
                <value>Common Stock</value>
            </securityTitle>
            <transactionDate>
                <value>2017-09-29</value>
            </transactionDate>
            <deemedExecutionDate></deemedExecutionDate>
            <transactionCoding>
                <transactionFormType>4</transactionFormType>
                <transactionCode>D</transactionCode>
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                <footnoteId id="F1"/>
            </transactionCoding>
            <transactionTimeliness>
                <value></value>
            </transactionTimeliness>
            <transactionAmounts>
                <transactionShares>
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                </transactionShares>
                <transactionPricePerShare>
                    <footnoteId id="F1"/>
                </transactionPricePerShare>
                <transactionAcquiredDisposedCode>
                    <value>D</value>
                </transactionAcquiredDisposedCode>
            </transactionAmounts>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>0</value>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>D</value>
                </directOrIndirectOwnership>
            </ownershipNature>
        </nonDerivativeTransaction>
    </nonDerivativeTable>

    <derivativeTable>
        <derivativeTransaction>
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            </securityTitle>
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            </conversionOrExercisePrice>
            <transactionDate>
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            </transactionDate>
            <deemedExecutionDate></deemedExecutionDate>
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            <transactionTimeliness>
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            <transactionAmounts>
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                </transactionShares>
                <transactionPricePerShare>
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                </transactionPricePerShare>
                <transactionAcquiredDisposedCode>
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                </transactionAcquiredDisposedCode>
            </transactionAmounts>
            <exerciseDate>
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            </exerciseDate>
            <expirationDate>
                <value>2017-12-31</value>
            </expirationDate>
            <underlyingSecurity>
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                </underlyingSecurityTitle>
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                </underlyingSecurityShares>
            </underlyingSecurity>
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                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
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                </directOrIndirectOwnership>
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        <derivativeTransaction>
            <securityTitle>
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            </conversionOrExercisePrice>
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            <expirationDate>
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                </underlyingSecurityTitle>
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            </underlyingSecurity>
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                </sharesOwnedFollowingTransaction>
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                </transactionShares>
                <transactionPricePerShare>
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                <transactionAcquiredDisposedCode>
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            <expirationDate>
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                <underlyingSecurityTitle>
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                </underlyingSecurityTitle>
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                </underlyingSecurityShares>
            </underlyingSecurity>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
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                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
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                </directOrIndirectOwnership>
            </ownershipNature>
        </derivativeTransaction>
        <derivativeTransaction>
            <securityTitle>
                <value>Restricted Stock Units</value>
            </securityTitle>
            <conversionOrExercisePrice>
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            </conversionOrExercisePrice>
            <transactionDate>
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            </transactionDate>
            <deemedExecutionDate></deemedExecutionDate>
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            <transactionTimeliness>
                <value></value>
            </transactionTimeliness>
            <transactionAmounts>
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                </transactionShares>
                <transactionPricePerShare>
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                </transactionPricePerShare>
                <transactionAcquiredDisposedCode>
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            </transactionAmounts>
            <exerciseDate>
                <value>2017-09-10</value>
            </exerciseDate>
            <expirationDate>
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            </expirationDate>
            <underlyingSecurity>
                <underlyingSecurityTitle>
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                </underlyingSecurityTitle>
                <underlyingSecurityShares>
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                </underlyingSecurityShares>
            </underlyingSecurity>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
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                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
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        </derivativeTransaction>
        <derivativeTransaction>
            <securityTitle>
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            <conversionOrExercisePrice>
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            </conversionOrExercisePrice>
            <transactionDate>
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            <deemedExecutionDate></deemedExecutionDate>
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            <transactionAmounts>
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                </transactionShares>
                <transactionPricePerShare>
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                <transactionAcquiredDisposedCode>
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            <transactionDate>
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        <derivativeTransaction>
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            </transactionDate>
            <deemedExecutionDate></deemedExecutionDate>
            <transactionCoding>
                <transactionFormType>4</transactionFormType>
                <transactionCode>U</transactionCode>
                <equitySwapInvolved>0</equitySwapInvolved>
                <footnoteId id="F3"/>
            </transactionCoding>
            <transactionTimeliness>
                <value></value>
            </transactionTimeliness>
            <transactionAmounts>
                <transactionShares>
                    <value>25400</value>
                </transactionShares>
                <transactionPricePerShare>
                    <value>21.10</value>
                </transactionPricePerShare>
                <transactionAcquiredDisposedCode>
                    <value>D</value>
                </transactionAcquiredDisposedCode>
            </transactionAmounts>
            <exerciseDate>
                <footnoteId id="F9"/>
            </exerciseDate>
            <expirationDate>
                <value>2024-09-14</value>
            </expirationDate>
            <underlyingSecurity>
                <underlyingSecurityTitle>
                    <value>Common Stock</value>
                </underlyingSecurityTitle>
                <underlyingSecurityShares>
                    <value>25400</value>
                </underlyingSecurityShares>
            </underlyingSecurity>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>0</value>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>D</value>
                </directOrIndirectOwnership>
            </ownershipNature>
        </derivativeTransaction>
    </derivativeTable>

    <footnotes>
        <footnote id="F1">Disposed of pursuant to the Agreement and Plan of Merger by and among PAREXEL International Corporation, West Street Parent, LLC and West Street Merger Sub, Inc., dated June 19, 2017 (the &quot;Merger Agreement&quot;), whereby, at the effective time of the merger contemplated therein (the &quot;Effective Time&quot;), all issued and outstanding shares of the Issuer's common stock were automatically cancelled and converted into the right to receive $88.10 per share in cash without interest (the &quot;Merger Consideration&quot;).</footnote>
        <footnote id="F2">Pursuant to the terms of the Merger Agreement, immediately prior to the Effective Time, each Company RSU Award, whether or not vested, was assumed by West Street Parent, LLC or the Company, cancelled and exchanged for the right to receive an amount in cash equal to the product obtained by multiplying (i) the aggregate number of shares of Company Common Stock subject to such award by (ii) the Merger Consideration.</footnote>
        <footnote id="F3">Pursuant to the terms of the Agreement and Plan of Merger by and among PAREXEL International Corporation, West Street Parent, LLC and West Street Merger Sub, Inc., dated June 19, 2017, each Company Stock Option, whether or not vested or exercisable, automatically converted into the right to receive an amount in cash equal to the product obtained by multiplying (i) the excess of the Merger Consideration over the per share exercise price of such Company Stock Option, by (ii) the aggregate number of shares of Company Common Stock issuable upon exercise of settlement of such Company Stock Option prior to the Effective Time.</footnote>
        <footnote id="F4">Options become exercisable in increments of 25% of the total shares granted, which commenced on the first anniversary of 09/21/2011.</footnote>
        <footnote id="F5">Options become exercisable in increments of 25% of the total shares granted, which commenced on the first anniversary of 09/19/2012.</footnote>
        <footnote id="F6">Options become exercisable in increments of 25% of the total shares granted, which commenced on the first anniversary of 09/11/2013.</footnote>
        <footnote id="F7">Options become exercisable in increments of 25% of the total shares granted, which commenced on the first anniversary of 09/10/2014.</footnote>
        <footnote id="F8">Options become exercisable in increments of 25% of the total shares granted, which commenced on the first anniversary of 09/09/2015.</footnote>
        <footnote id="F9">Options become exercisable in increments of 25% of the total shares granted, which commenced on the first anniversary of 09/14/2016.</footnote>
    </footnotes>

    <remarks></remarks>

    <ownerSignature>
        <signatureName>/s/ Douglas Batt, as Attorney-in-Fact</signatureName>
        <signatureDate>2017-10-04</signatureDate>
    </ownerSignature>
</ownershipDocument>
