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Proc-Type: 2001,MIC-CLEAR
Originator-Name: webmaster@www.sec.gov
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 TWSM7vrzLADbmYQaionwg5sDW3P6oaM5D3tdezXMm7z1T+B+twIDAQAB
MIC-Info: RSA-MD5,RSA,
 SHQND1Mg9HA3fpZvEZWpDHii6u/jMFYrxDaJcPqQBhx/c1vivX5jNZdPPyk54kSc
 uuT2+IkhBkoYLKMzqx9NOQ==

<SEC-DOCUMENT>0001127602-09-012357.txt : 20090527
<SEC-HEADER>0001127602-09-012357.hdr.sgml : 20090527
<ACCEPTANCE-DATETIME>20090527173427
ACCESSION NUMBER:		0001127602-09-012357
CONFORMED SUBMISSION TYPE:	4
PUBLIC DOCUMENT COUNT:		1
CONFORMED PERIOD OF REPORT:	20090526
FILED AS OF DATE:		20090527
DATE AS OF CHANGE:		20090527

REPORTING-OWNER:	

	OWNER DATA:	
		COMPANY CONFORMED NAME:			SANDNESS PAUL K
		CENTRAL INDEX KEY:			0001285204

	FILING VALUES:
		FORM TYPE:		4
		SEC ACT:		1934 Act
		SEC FILE NUMBER:	001-03480
		FILM NUMBER:		09855497

	MAIL ADDRESS:	
		STREET 1:		918 EAST DIVID AVE
		STREET 2:		PO BOX 5650
		CITY:			BISMARCK
		STATE:			ND
		ZIP:			58506-5350

ISSUER:		

	COMPANY DATA:	
		COMPANY CONFORMED NAME:			MDU RESOURCES GROUP INC
		CENTRAL INDEX KEY:			0000067716
		STANDARD INDUSTRIAL CLASSIFICATION:	MINING, QUARRYING OF NONMETALLIC MINERALS (NO FUELS) [1400]
		IRS NUMBER:				410423660
		STATE OF INCORPORATION:			DE
		FISCAL YEAR END:			1231

	BUSINESS ADDRESS:	
		STREET 1:		1200 WEST CENTURY AVENUE
		CITY:			BISMARCK
		STATE:			ND
		ZIP:			58506-5650
		BUSINESS PHONE:		701-530-1059

	MAIL ADDRESS:	
		STREET 1:		1200 WEST CENTURY AVENUE
		CITY:			BISMARCK
		STATE:			ND
		ZIP:			58506-5650

	FORMER COMPANY:	
		FORMER CONFORMED NAME:	MONTANA DAKOTA UTILITIES CO
		DATE OF NAME CHANGE:	19850429
</SEC-HEADER>
<DOCUMENT>
<TYPE>4
<SEQUENCE>1
<FILENAME>form4.xml
<DESCRIPTION>PRIMARY DOCUMENT
<TEXT>
<XML>
<?xml version="1.0"?>
<ownershipDocument>

    <schemaVersion>X0303</schemaVersion>

    <documentType>4</documentType>

    <periodOfReport>2009-05-26</periodOfReport>

    <issuer>
        <issuerCik>0000067716</issuerCik>
        <issuerName>MDU RESOURCES GROUP INC</issuerName>
        <issuerTradingSymbol>MDU</issuerTradingSymbol>
    </issuer>

    <reportingOwner>
        <reportingOwnerId>
            <rptOwnerCik>0001285204</rptOwnerCik>
            <rptOwnerName>SANDNESS PAUL K</rptOwnerName>
        </reportingOwnerId>
        <reportingOwnerAddress>
            <rptOwnerStreet1>MDU RESOURCES GROUP, INC.</rptOwnerStreet1>
            <rptOwnerStreet2>P. O. BOX 5650</rptOwnerStreet2>
            <rptOwnerCity>BISMARCK</rptOwnerCity>
            <rptOwnerState>ND</rptOwnerState>
            <rptOwnerZipCode>58506-5650</rptOwnerZipCode>
            <rptOwnerStateDescription></rptOwnerStateDescription>
        </reportingOwnerAddress>
        <reportingOwnerRelationship>
            <isOfficer>1</isOfficer>
            <officerTitle>General Counsel and Secretary</officerTitle>
        </reportingOwnerRelationship>
    </reportingOwner>

    <nonDerivativeTable>
        <nonDerivativeTransaction>
            <securityTitle>
                <value>Common Stock</value>
            </securityTitle>
            <transactionDate>
                <value>2009-05-26</value>
            </transactionDate>
            <transactionCoding>
                <transactionFormType>4</transactionFormType>
                <transactionCode>P</transactionCode>
                <equitySwapInvolved>0</equitySwapInvolved>
            </transactionCoding>
            <transactionTimeliness></transactionTimeliness>
            <transactionAmounts>
                <transactionShares>
                    <value>277.778</value>
                </transactionShares>
                <transactionPricePerShare>
                    <value>18.00</value>
                </transactionPricePerShare>
                <transactionAcquiredDisposedCode>
                    <value>A</value>
                </transactionAcquiredDisposedCode>
            </transactionAmounts>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>24297.509</value>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>D</value>
                </directOrIndirectOwnership>
            </ownershipNature>
        </nonDerivativeTransaction>
        <nonDerivativeHolding>
            <securityTitle>
                <value>Common Stock - (401-k)</value>
            </securityTitle>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>11636.396</value>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>I</value>
                </directOrIndirectOwnership>
                <natureOfOwnership>
                    <value>By Trustee</value>
                </natureOfOwnership>
            </ownershipNature>
        </nonDerivativeHolding>
    </nonDerivativeTable>

    <footnotes></footnotes>

    <ownerSignature>
        <signatureName>/s/ Paul K. Sandness</signatureName>
        <signatureDate>2009-05-27</signatureDate>
    </ownerSignature>
</ownershipDocument>
</XML>
</TEXT>
</DOCUMENT>
</SEC-DOCUMENT>
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