EXHIBIT 5(b)










                                                                    Exhibit 5(b)




                     LeBoeuf, Lamb, Greene & MacRae, L.L.P.
                              125 West 55th Street
                             New York, NY 10019-5389






                                                   September 28, 2001

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 preparation and filing with
the Securities and Exchange Commission (the "Commission") under the Securities
Act of 1933, as amended (the "Securities Act"), of the Company's registration
statement on Form S-8 (the "Registration Statement") relating to the
registration of 2,600,000 additional shares of its Common Stock, par value $1.00
(the "Stock") and the Preference Share Purchase Rights attached thereto (the
"Rights"),for offer and sale in connection with the MDU Resources Group, Inc.
401(k) Retirement Plan (the "Plan").

     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 Norwest Bank, Minnesota, N.A., as Rights Agent, together with the
exhibits thereto (the "Rights Agreement"), pursuant to which the Rights were
created, (iii) resolutions of the Board of Directors of the Company, dated July
18, 2001, authorizing the issuance of the Stock pursuant to the Plan, (iv) the
Plan, (v) the orders of the Federal Energy Regulatory Commission dated September
4, 2001, the Montana Public Service Commission dated August 21, 2001, and the
Public Service Commission of Wyoming dated August 27, 2001, and (vi) such other
instruments, certificates, records and documents, and such matters of law, as we
have considered necessary or appropriate for the purposes hereof. In such
examination, we have assumed the genuineness of all signatures, the authenticity
of all documents submitted to us as originals, the conformity to the original
documents of all documents submitted to us as copies and the authenticity of the
originals of such latter documents. As to any facts material to our opinion, we
have, when





relevant facts were not independently established, relied upon the aforesaid
Registration Statement, Rights Agreement, resolutions, orders, instruments,
certificates, records and documents. We have also assumed the regularity of all
corporate procedures.

     Based upon the foregoing, and subject to the limitations and qualifications
contained in this opinion, we are of the opinion that:

     1.   When

          (a)  appropriate authorizations by the Federal Energy Regulatory
               Commission, the Montana Public Service Commission and the Public
               Service Commission of Wyoming with respect to the issuance and
               sale of the Stock shall have been granted,

          (b)  the Company's Board of Directors shall have approved the issuance
               and sale of the Stock by the Company,

          (c)  the Registration Statement shall have become effective under the
               Securities Act and

          (d)  the Stock shall have been issued, delivered and paid for in
               accordance with the terms of the Plan and the corporate and
               governmental authorizations and instruments referred to above,

the Stock will be duly authorized, validly issued, fully paid and
non-assessable.

     2. The Rights, when issued in accordance with the terms of the Rights
Agreement, will be validly issued and will represent legally binding obligations
of the Company under the laws of the State of Delaware.

     We express no opinion with respect to any laws other than 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. Insofar as this
opinion involves matters of the laws of the States of Montana, North Dakota and
Wyoming, we have relied upon the opinion of even date herewith addressed to you
by Lester H. Loble, II, Vice President, General Counsel and Secretary of the
Company.





     We hereby consent to the use of this opinion as an exhibit to the
Registration Statement. In giving such consent, we do not thereby concede that
we are within 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/LeBoeuf, Lamb, Greene & MacRae, L.L.P.