Exhibit 5(b)

                    [LETTERHEAD OF THELEN REID & PRIEST LLP]


                                  June 13, 2003




MDU Resources Group, Inc.
Schuchart Building
918 East Divide Avenue
P.O. Box 5650 Bismarck, North Dakota 58506-5650

Ladies and Gentlemen:

     We are acting as counsel for MDU Resources Group, Inc., a Delaware
corporation (the "Company"), in connection with the Registration Statement on
Form S-3, SEC File No. 333-104150 (the "Registration Statement") to be filed on
or about the date hereof with the Securities and Exchange Commission (the
"Commission") by the Company under the Securities Act of 1933, as amended (the
"Securities Act"), for the registration of the sale by the Company from time to
time of up to $500,000,000 in aggregate amount of (i) debt securities (the "Debt
Securities") and (ii) common stock, par value $1.00 per share (the "Stock")
together with the preference share purchase rights attached thereto (the
"Rights").

     In connection with this opinion, we have examined originals or copies,
certified or otherwise identified to our satisfaction, of (i) the Registration
Statement, (ii) the Rights Agreement, dated as of November 12, 1998, between the
Company and Wells Fargo Bank, Minnesota, N.A. (formerly, Norwest Bank Minnesota,
N.A.), as Rights Agent, together with the exhibits thereto, pursuant to which
the Rights were created, (iii) the orders of the Federal Energy Regulatory
Commission, dated November 1, 2002, the Montana Public Service Commission, dated
November 19, 2002, and the Public Service Commission of Wyoming, dated November
14, 2002 (collectively, the "Orders"), and (iv) such other instruments,
certificates, records and documents, and such matters of law, as we have
considered necessary or appropriate for the purposes hereof.

     Based on the foregoing, subject to the limitations and qualifications
contained in this opinion, and provided the Orders remain in full force and
effect and have not been amended, rescinded or repealed, we are of the opinion
that:

     1.   The Company is a corporation validly organized and existing under the
          laws of the State of Delaware.

     2.   When

     (a)  the Registration Statement shall have become effective under the
          Securities Act,

     (b)  an Indenture between the Company and the Bank of New York in
          substantially the form attached to the Registration Statement as
          Exhibit 4(d) (the "Indenture") with respect to the Debt Securities
          shall have been executed and delivered by a duly authorized officer or
          representative of the Company and by the trustee under such Indenture;
          and

     (c)  the Board of Directors of the Company, or an officer duly authorized
          thereby, shall have taken such action, pursuant to the terms of the
          Indenture, as may be necessary to establish the terms of such Debt
          Securities, and such Debt Securities shall have been issued and
          delivered in accordance with the terms and provisions of such
          Indenture,

          the Debt Securities will be legally issued and valid and binding
          obligations of the Company.

     3.   When

     (a)  the Registration Statement shall have become effective under the
          Securities Act,

     (b)  the Company's Board of Directors or a duly authorized committee
          thereof shall have (i) approved the issuance and sale of the Stock by
          the Company, (ii) fixed or otherwise determined the consideration to
          be received therefor, (iii) approved the form and substance of the
          documents to be used in connection with the issuance and sale of such
          Stock (the "Stock Sale Documents"), and (iv) taken, or delegated to
          appropriate officers or representatives of the Company the authority
          to take and, pursuant thereto, such officers or representatives shall
          have taken, all other final action necessary to consummate the
          authorization of the issuance and sale of such Stock,

     (c)  the Stock Sale Documents shall have been duly executed and delivered
          by or on behalf of the parties thereto and shall have become effective
          as therein provided, and

     (d)  the Stock shall have been duly issued and delivered by the Company for
          the consideration set forth in the Registration Statement and in
          accordance with the actions hereinabove mentioned,

     the Stock will be legally issued, fully paid and non-assessable.

     4.   The Rights, when issued as contemplated in the Registration Statement,
          will be legally issued and will represent binding obligations of the
          Company under the laws of the State of Delaware.

     Our opinions expressed above are limited to the law of the State of New
York, the General Corporation Law of the State of Delaware, the applicable
provisions of the Delaware Constitution and the reported judicial decisions
interpreting the Delaware laws and the federal laws of the United States of
America.

     We hereby consent to the use of this opinion as an exhibit to the
Registration Statement and to the use of our name, as counsel, therein. In
giving the foregoing consent, we do not thereby admit that we are in the
category of persons whose consent is required under Section 7 of the Securities
Act or the rules and regulations of the Commission thereunder.

                                                         Very truly yours,

                                                    /s/ Thelen Reid & Priest LLP
                                                    ----------------------------
                                                      THELEN REID & PRIEST LLP