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

    <schemaVersion>X0306</schemaVersion>

    <documentType>4</documentType>

    <periodOfReport>2020-06-16</periodOfReport>

    <notSubjectToSection16>0</notSubjectToSection16>

    <issuer>
        <issuerCik>0001176984</issuerCik>
        <issuerName>EATON VANCE MUNICIPAL BOND FUND</issuerName>
        <issuerTradingSymbol>EIM</issuerTradingSymbol>
    </issuer>

    <reportingOwner>
        <reportingOwnerId>
            <rptOwnerCik>0001223048</rptOwnerCik>
            <rptOwnerName>KARPUS GEORGE W</rptOwnerName>
        </reportingOwnerId>
        <reportingOwnerAddress>
            <rptOwnerStreet1>C/O KARPUS INVESTMENT MANAGEMENT</rptOwnerStreet1>
            <rptOwnerStreet2>183 SULLY'S TRAIL</rptOwnerStreet2>
            <rptOwnerCity>PITTSFORD</rptOwnerCity>
            <rptOwnerState>NY</rptOwnerState>
            <rptOwnerZipCode>14534</rptOwnerZipCode>
            <rptOwnerStateDescription></rptOwnerStateDescription>
        </reportingOwnerAddress>
        <reportingOwnerRelationship>
            <isDirector>0</isDirector>
            <isOfficer>0</isOfficer>
            <isTenPercentOwner>1</isTenPercentOwner>
            <isOther>0</isOther>
        </reportingOwnerRelationship>
    </reportingOwner>

    <nonDerivativeTable>
        <nonDerivativeTransaction>
            <securityTitle>
                <value>Common Stock</value>
                <footnoteId id="F1"/>
            </securityTitle>
            <transactionDate>
                <value>2020-06-16</value>
            </transactionDate>
            <transactionCoding>
                <transactionFormType>4</transactionFormType>
                <transactionCode>S</transactionCode>
                <equitySwapInvolved>0</equitySwapInvolved>
            </transactionCoding>
            <transactionTimeliness>
                <value></value>
            </transactionTimeliness>
            <transactionAmounts>
                <transactionShares>
                    <value>3700</value>
                    <footnoteId id="F2"/>
                </transactionShares>
                <transactionPricePerShare>
                    <value>12.71</value>
                </transactionPricePerShare>
                <transactionAcquiredDisposedCode>
                    <value>D</value>
                </transactionAcquiredDisposedCode>
            </transactionAmounts>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>526839</value>
                    <footnoteId id="F3"/>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>D</value>
                </directOrIndirectOwnership>
            </ownershipNature>
        </nonDerivativeTransaction>
        <nonDerivativeTransaction>
            <securityTitle>
                <value>Common Stock</value>
                <footnoteId id="F1"/>
            </securityTitle>
            <transactionDate>
                <value>2020-06-17</value>
            </transactionDate>
            <transactionCoding>
                <transactionFormType>4</transactionFormType>
                <transactionCode>S</transactionCode>
                <equitySwapInvolved>0</equitySwapInvolved>
            </transactionCoding>
            <transactionTimeliness>
                <value></value>
            </transactionTimeliness>
            <transactionAmounts>
                <transactionShares>
                    <value>30488</value>
                    <footnoteId id="F2"/>
                </transactionShares>
                <transactionPricePerShare>
                    <value>12.65</value>
                </transactionPricePerShare>
                <transactionAcquiredDisposedCode>
                    <value>D</value>
                </transactionAcquiredDisposedCode>
            </transactionAmounts>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>496351</value>
                    <footnoteId id="F3"/>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>D</value>
                </directOrIndirectOwnership>
            </ownershipNature>
        </nonDerivativeTransaction>
    </nonDerivativeTable>

    <footnotes>
        <footnote id="F1">This Form 4 is filed by George W. Karpus (the &quot;Reporting Person&quot;). The Reporting Person may be deemed to be a member of a Section 13(d) group that beneficially owns in the aggregate more than 10% of the Issuer's outstanding shares of common stock. This Form 4 reports transactions in shares of common stock of the Issuer in which the Reporting Person has a pecuniary interest.</footnote>
        <footnote id="F2">Represents transactions in shares of common stock of the Issuer held directly by the Reporting Person and a corporate account maintained by Karpus Management, Inc. (the &quot;Karpus Account&quot;). The Reporting Person disclaims beneficial ownership of such shares except to the extent of his pecuniary interest therein. Karpus Management, Inc. may also be deemed to have a pecuniary interest in the Karpus Account.</footnote>
        <footnote id="F3">Excludes shares of common stock of the Issuer held directly by The Karpus Family Foundation, Inc. and Karpus Investment Management Profit Sharing Plan Fund B - Conservative Bond Fund. The Reporting Person does not have a pecuniary interest in such shares.</footnote>
    </footnotes>

    <ownerSignature>
        <signatureName>George W. Karpus</signatureName>
        <signatureDate>2020-06-18</signatureDate>
    </ownerSignature>
</ownershipDocument>
