-----BEGIN PRIVACY-ENHANCED MESSAGE-----
Proc-Type: 2001,MIC-CLEAR
Originator-Name: webmaster@www.sec.gov
Originator-Key-Asymmetric:
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 TWSM7vrzLADbmYQaionwg5sDW3P6oaM5D3tdezXMm7z1T+B+twIDAQAB
MIC-Info: RSA-MD5,RSA,
 SsZ0g4j0/DKiPAkPUobFqd+JyhlLdb/DNBnOBAJdopf1/7HMhEaJ/QPFzF2HukES
 f4z5glH9/VsdaGahvQ8pqg==

<SEC-DOCUMENT>0001240480-07-000002.txt : 20070326
<SEC-HEADER>0001240480-07-000002.hdr.sgml : 20070326
<ACCEPTANCE-DATETIME>20070326104223
ACCESSION NUMBER:		0001240480-07-000002
CONFORMED SUBMISSION TYPE:	4
PUBLIC DOCUMENT COUNT:		1
CONFORMED PERIOD OF REPORT:	20070323
FILED AS OF DATE:		20070326
DATE AS OF CHANGE:		20070326

ISSUER:		

	COMPANY DATA:	
		COMPANY CONFORMED NAME:			WESTERN ASSET MUNICIPAL HIGH INCOME FUND INC.
		CENTRAL INDEX KEY:			0000830487
		STANDARD INDUSTRIAL CLASSIFICATION:	UNKNOWN SIC - 0000 [0000]
		IRS NUMBER:				000000000
		FISCAL YEAR END:			1031

	BUSINESS ADDRESS:	
		STREET 1:		CITIGROUP ASSET MANAGEMENT
		STREET 2:		125 BROAD STREET, 10TH FLOOR
		CITY:			NEW YORK
		STATE:			NY
		ZIP:			10004
		BUSINESS PHONE:		212-291-2556

	MAIL ADDRESS:	
		STREET 1:		CITIGROUP ASSET MANAGEMENT
		STREET 2:		125 BROAD STREET, 10TH FLOOR
		CITY:			NEW YORK
		STATE:			NY
		ZIP:			10004

	FORMER COMPANY:	
		FORMER CONFORMED NAME:	MUNICIPAL HIGH INCOME FUND INC
		DATE OF NAME CHANGE:	19920703

	FORMER COMPANY:	
		FORMER CONFORMED NAME:	SPECIAL OPPORTUNITIES MUNICIPAL FUND INC
		DATE OF NAME CHANGE:	19881025

REPORTING-OWNER:	

	OWNER DATA:	
		COMPANY CONFORMED NAME:			CRONIN DANIEL P
		CENTRAL INDEX KEY:			0001240480

	FILING VALUES:
		FORM TYPE:		4
		SEC ACT:		1934 Act
		SEC FILE NUMBER:	811-05497
		FILM NUMBER:		07716864

	BUSINESS ADDRESS:	
		STREET 1:		PFIZER INC
		STREET 2:		235 EAST 42ND ST
		CITY:			NEW YORK
		STATE:			NY
		ZIP:			10017

	MAIL ADDRESS:	
		STREET 1:		235 EAST 42ND ST
		CITY:			NEW YORK
		STATE:			NY
		ZIP:			10017
</SEC-HEADER>
<DOCUMENT>
<TYPE>4
<SEQUENCE>1
<FILENAME>primary_doc.xml
<DESCRIPTION>PRIMARY DOCUMENT
<TEXT>
<XML>
<?xml version="1.0"?>
<ownershipDocument>

    <schemaVersion>X0202</schemaVersion>

    <documentType>4</documentType>

    <periodOfReport>2007-03-23</periodOfReport>

    <notSubjectToSection16>0</notSubjectToSection16>

    <issuer>
        <issuerCik>0000830487</issuerCik>
        <issuerName>WESTERN ASSET MUNICIPAL HIGH INCOME FUND INC.</issuerName>
        <issuerTradingSymbol>MHF</issuerTradingSymbol>
    </issuer>

    <reportingOwner>
        <reportingOwnerId>
            <rptOwnerCik>0001240480</rptOwnerCik>
            <rptOwnerName>CRONIN DANIEL P</rptOwnerName>
        </reportingOwnerId>
        <reportingOwnerAddress>
            <rptOwnerStreet1>235 EAST 42ND ST</rptOwnerStreet1>
            <rptOwnerStreet2></rptOwnerStreet2>
            <rptOwnerCity>NEW YORK</rptOwnerCity>
            <rptOwnerState>NY</rptOwnerState>
            <rptOwnerZipCode>10017</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>2007-03-23</value>
            </transactionDate>
            <transactionCoding>
                <transactionFormType>4</transactionFormType>
                <transactionCode>P</transactionCode>
                <equitySwapInvolved>0</equitySwapInvolved>
            </transactionCoding>
            <transactionTimeliness>
                <value></value>
            </transactionTimeliness>
            <transactionAmounts>
                <transactionShares>
                    <value>2300</value>
                </transactionShares>
                <transactionPricePerShare>
                    <value>8.02</value>
                </transactionPricePerShare>
                <transactionAcquiredDisposedCode>
                    <value>A</value>
                </transactionAcquiredDisposedCode>
            </transactionAmounts>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>2300</value>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>D</value>
                </directOrIndirectOwnership>
            </ownershipNature>
        </nonDerivativeTransaction>
    </nonDerivativeTable>

    <ownerSignature>
        <signatureName>William J. Renahan by Power of Attorney for Daniel P. Cronin</signatureName>
        <signatureDate>2007-03-26</signatureDate>
    </ownerSignature>
</ownershipDocument>
</XML>
</TEXT>
</DOCUMENT>
</SEC-DOCUMENT>
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