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

    <schemaVersion>X0306</schemaVersion>

    <documentType>4</documentType>

    <periodOfReport>2015-12-04</periodOfReport>

    <notSubjectToSection16>0</notSubjectToSection16>

    <issuer>
        <issuerCik>0000726517</issuerCik>
        <issuerName>MERCHANTS BANCSHARES INC</issuerName>
        <issuerTradingSymbol>MBVT</issuerTradingSymbol>
    </issuer>

    <reportingOwner>
        <reportingOwnerId>
            <rptOwnerCik>0001247473</rptOwnerCik>
            <rptOwnerName>CHASE DONALD R</rptOwnerName>
        </reportingOwnerId>
        <reportingOwnerAddress>
            <rptOwnerStreet1>39 TIMBER RIDGE RD.</rptOwnerStreet1>
            <rptOwnerStreet2></rptOwnerStreet2>
            <rptOwnerCity>WEST SPRINGFIELD</rptOwnerCity>
            <rptOwnerState>MA</rptOwnerState>
            <rptOwnerZipCode>01089</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>2015-12-04</value>
            </transactionDate>
            <transactionCoding>
                <transactionFormType>4</transactionFormType>
                <transactionCode>A</transactionCode>
                <equitySwapInvolved>0</equitySwapInvolved>
            </transactionCoding>
            <transactionTimeliness>
                <value></value>
            </transactionTimeliness>
            <transactionAmounts>
                <transactionShares>
                    <value>29648</value>
                </transactionShares>
                <transactionPricePerShare>
                    <footnoteId id="F1"/>
                </transactionPricePerShare>
                <transactionAcquiredDisposedCode>
                    <value>A</value>
                </transactionAcquiredDisposedCode>
            </transactionAmounts>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>29648</value>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>D</value>
                </directOrIndirectOwnership>
            </ownershipNature>
        </nonDerivativeTransaction>
    </nonDerivativeTable>

    <footnotes>
        <footnote id="F1">(1) Received in exchange for 122,724 shares of NUVO Bank &amp; Trust Company (&quot;NUVO&quot;) common stock in connection with the acquisition of NUVO by Merchants Bancshares, Inc. (the &quot;Merger&quot;).  On the effective date of the Merger, the closing price of Merchants Bancshares, Inc.'s common stock was $32.66 per share.</footnote>
    </footnotes>

    <ownerSignature>
        <signatureName>/s/ Jodi L. Bachand, POA for Donald R. Chase</signatureName>
        <signatureDate>2016-03-30</signatureDate>
    </ownerSignature>
</ownershipDocument>
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X0306
4
2015-12-04
0
0000726517
MERCHANTS BANCSHARES INC
MBVT
0001247473
CHASE DONALD R
39 TIMBER RIDGE RD.
WEST SPRINGFIELD
MA
01089
1
0
0
0
Common Stock
2015-12-04
4
A
0
29648
A
29648
D
(1) Received in exchange for 122,724 shares of NUVO Bank & Trust Company ("NUVO") common stock in connection with the acquisition of NUVO by Merchants Bancshares, Inc. (the "Merger").  On the effective date of the Merger, the closing price of Merchants Bancshares, Inc.'s common stock was $32.66 per share.
/s/ Jodi L. Bachand, POA for Donald R. Chase
2016-03-30