EXHIBIT 5(a)








                                                                  Exhibit 5(a)

                             Paul K. Sandness, Esq.
                          General Counsel and Secretary
                            MDU Resources Group, Inc.
                     1200 West Century Avenue, P.O. Box 5650
                        Bismarck, North Dakota 58506-5650




                                                           December 6, 2006



MDU Resources Group, Inc.
1200 West Century Avenue, P.O. Box 5650
Bismarck, North Dakota  58506-5650

Ladies and Gentlemen:

     I am General Counsel and Secretary of MDU Resources Group, Inc., a Delaware
corporation (the "Company"). This opinion is being rendered in connection with
the Registration Statement on Form S-8 (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 2,600,000 shares of its common
stock, par value $1.00 per share (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.

     In connection with this opinion, I have examined originals or copies,
certified or otherwise identified to my satisfaction, of (i) the Registration
Statement, (ii) the Rights Agreement, dated as of November 12, 1998, between the
Company and Wells Fargo Bank, N.A. (formerly known as Norwest Bank Minnesota,
N.A.), as Rights Agent, together with the exhibits thereto (the "Rights
Agreement"), pursuant to which the Rights were created, (iii) the Restated
Certificate of Incorporation, as amended, and the Bylaws, as amended, of the
Company, as in effect on the date hereof, (iv) resolutions of the Board of
Directors of the Company, dated May 11, 2006, authorizing the issuance of the
Stock, (v) the Order of the Federal Energy Regulatory Commission, dated November
29, 2006, authorizing the issuance of the Stock, (vi) the Default Order of the
Public Service Commission of the State of Montana, dated November 9, 2006,
authorizing the issuance of the Stock, (vii) the Order of the Public Service
Commission of Wyoming, dated December 4, 2006, authorizing the issuance of the
Stock and (viii) such other instruments, certificates, records and documents,
and such matters of law, as I have considered necessary or appropriate for the
purposes hereof.

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





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

     2. The issuance of the Stock has been duly authorized by the Board of
Directors of the Company.

     3. The Federal Energy Regulatory Commission, the Montana Public Service
Commission and the Public Service Commission of Wyoming have issued orders
authorizing the issuance and sale of the Stock; provided that such orders remain
in full force and effect and have not been amended, rescinded or repealed, upon
issuance and delivery of the Stock and the receipt by the Company of the
consideration therefor, as set forth in the Plan, the Stock will be validly
issued, fully paid and non-assessable.

     4. The issuance of the Rights has been duly authorized by all necessary
corporate action on the part of the Company and, when issued and delivered in
accordance with the Rights Agreement, the Rights will be validly issued.

     Insofar as the opinions expressed herein relate to 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,
or the federal laws of the United States of America, I have relied on the
opinion of even date herewith of LeBoeuf, Lamb, Greene & MacRae LLP, counsel to
the Company, which opinion is to be filed as an exhibit to the Registration
Statement.

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

                                           Very truly yours,

                                           /s/  Paul K. Sandness
                                           ------------------------------------
                                           Paul K. Sandness
                                           General Counsel and
                                           Secretary