As filed with the Securities and Exchange Commission on March 24, 2000.
                                                      Registration No. 333-27879
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                       SECURITIES AND EXCHANGE COMMISSION
                             WASHINGTON, D.C. 20549

                       ----------------------------------

                                 POST-EFFECTIVE
                                 AMENDMENT NO. 1
                                       TO
                                    FORM S-8
                             REGISTRATION STATEMENT
                                      UNDER
                           THE SECURITIES ACT OF 1933

                       ----------------------------------

                            MDU RESOURCES GROUP, INC.
             (Exact name of registrant as specified in its charter)

          Delaware                                              No. 41-0423660
(State or other jurisdiction of                                (I.R.S. Employer
 incorporation or organization)                              Identification No.)

                               Schuchart Building
                             918 East Divide Avenue
                                  P.O. Box 5650
                        Bismarck, North Dakota 58506-5650
          (Address of principal executive offices, including zip code)

                       ----------------------------------

                            MDU RESOURCES GROUP, INC.
                            1997 EXECUTIVE LONG-TERM
                                 INCENTIVE PLAN
                            (Full title of the plan)

                       ----------------------------------

                               Warren L. Robinson
                       Executive Vice President, Treasurer
                           and Chief Financial Officer
                            MDU Resources Group, Inc.
                               Schuchart Building
                             918 East Divide Avenue
                                  P.O. Box 5650
                        Bismarck, North Dakota 58506-5650
                                 (701) 222-7900

 (Name, address and telephone number, including area code, of agent for service)

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                                     PART II

               INFORMATION REQUIRED IN THE REGISTRATION STATEMENT

Item 3.  Incorporation of Documents by Reference.

     The following  documents,  which MDU Resources Group,  Inc. (the "Company")
has filed with the Securities and Exchange Commission pursuant to the Securities
Exchange Act of 1934, as amended (the "Exchange Act"),  are hereby  incorporated
by reference in this registration statement:

     1.  Annual  Report  on Form  10-K for the year  ended  December  31,  1999,
including  those portions of the Annual Report to  Stockholders  incorporated by
reference therein.

     2.  Description  of the Company's  common stock  contained in the Company's
registration  statement on Form 8-A/A,  dated March 23, 2000, and any amendments
thereto.

     3. Description of the Company's  preference share purchase rights contained
in the  registration  statement  on Form 8-A/A,  dated March 23,  2000,  and any
amendments thereto.

     All documents  subsequently filed by the Company pursuant to Section 13(a),
13(c), 14 or 15(d) of the Exchange Act, prior to the filing of a  post-effective
amendment  which  indicates that all securities  offered have been sold or which
deregisters  all  securities  then  remaining  unsold,  shall  be  deemed  to be
incorporated by reference in this  registration  statement and to be part hereof
from the date of filing of such documents. Any statement contained in a document
incorporated or deemed to be incorporated by reference herein shall be deemed to
be modified or superseded for the purposes of this registration statement to the
extent  that a statement  contained  herein or in any other  subsequently  filed
document  which  also is or is deemed to be  incorporated  by  reference  herein
modifies  or  supersedes  such  statement.  Any such  statement  so  modified or
superseded  shall  not be  deemed,  except  as so  modified  or  superseded,  to
constitute a part of this registration statement.

Item 8.  Exhibits.

     *4(a)     Restated  Certificate of Incorporation,  filed as Exhibit 3(a) to
               the Company's Quarterly Report on Form 10-Q for the quarter ended
               June 30, 1999, in File No. 1-3480.

     *4(b)     By-laws of the Company, as amended to date, filed as Exhibit 3(b)
               to the  Company's  Quarterly  Report on Form 10-Q for the quarter
               ended September 30, 1998, in File No. 1-3480.

     *4(c)     Rights  Agreement,  dated as of November  12,  1998,  between the
               Company and Norwest Bank Minnesota, N.A., filed as Exhibit 4.1 to
               Form 8-A on November 12, 1998, in File No. 1-3480.

- ----------
*Incorporated herein by reference as indicated.

                                      II-1


      5(a)     Opinion of Lester H.  Loble,  II,  Esq.,  General  Counsel to the
               Company.

      5(b)     Opinion of LeBoeuf, Lamb, Greene & MacRae, L.L.P., counsel to the
               Company.

     23(a)     Consent of Arthur Andersen LLP.

     23(b)     Consent of Lester H. Loble, II, Esq.  (contained in opinion filed
               as Exhibit 5(a) hereto).

     23(c)     Consent of LeBoeuf,  Lamb, Greene & MacRae, L.L.P.  (contained in
               opinion filed as Exhibit 5(b) hereto).

                                      II-2


                                   SIGNATURES

     The Registrant. Pursuant to the requirements of the Securities Act of 1933,
the registrant certifies that it has reasonable grounds to believe that it meets
all of the  requirements  for  filing  on  Form  S-8 and has  duly  caused  this
post-effective  amendment  to the  registration  statement  to be  signed on its
behalf by the undersigned,  thereunto duly authorized,  in the City of Bismarck,
State of North Dakota, on the 23rd day of March, 2000.

                                       MDU RESOURCES GROUP, INC.


                                       By: /s/ Martin A. White
                                           -----------------------------
                                           Martin A. White
                                           President and Chief Executive Officer

     Pursuant  to  the   requirements  of  the  Securities  Act  of  1933,  this
post-effective  amendment to the  registration  statement has been signed by the
following persons in the capacities and on the date indicated.

     Signature                               Title                     Date
     ---------                               -----                     ----

/s/ Martin A. White                Chief Executive Officer and    March 23, 2000
- --------------------------------     Director
Martin A. White
(President and Chief
Executive Officer)

         *                         Chief Administrative and       March 23, 2000
- --------------------------------     Corporate Development
Douglas C. Kane                      Officer and Director
(Executive Vice President, Chief
Administrative and Corporate
Development Officer)

/s/ Warren L. Robinson             Chief Financial Officer        March 23, 2000
- --------------------------------
Warren L. Robinson
(Executive Vice President,
Treasurer and Chief Financial
Officer)

         *                         Chief Accounting Officer       March 23, 2000
- --------------------------------
Vernon A. Raile
(Vice President, Controller and
Chief Accounting Officer)

                                      II-3


     Signature                               Title                     Date
     ---------                               -----                     ----

         *                                 Director               March 23, 2000
John A. Schuchart
- --------------------------------
(Chairman of the Board)

         *                                 Director               March 23, 2000
- --------------------------------
San W. Orr, Jr.
(Vice Chairman of the Board)

         *                                 Director               March 23, 2000
- --------------------------------
Thomas Everist

         *                                 Director               March 23, 2000
- --------------------------------
Richard L. Muus

         *                                 Director               March 23, 2000
- --------------------------------
Robert L. Nance

         *                                 Director               March 23, 2000
- --------------------------------
John L. Olson

         *                                 Director               March 23, 2000
- --------------------------------
Harry J. Pearce

         *                                 Director               March 23, 2000
- --------------------------------
Homer A. Scott, Jr.

         *                                 Director               March 23, 2000
- --------------------------------
Joseph T. Simmons

         *                                 Director               March 23, 2000
- --------------------------------
Sister Thomas Welder, O.S.B.


*By:  /s/ Warren L. Robinson                                      March 23, 2000
      --------------------------
        Warren L. Robinson
        as Attorney-in-fact
        for each of the persons
        indicated by an asterisk

                                      II-4


                                  EXHIBIT INDEX

     *4(a)         Restated Certificate of Incorporation, filed as Exhibit
                   3(a) to the Company's Quarterly Report on Form 10-Q
                   for the quarter ended  June 30, 1999, in File No. 1-3480.

     *4(b)         By-laws of the Company, as amended to date, filed as
                   Exhibit 3(b) to the Company's Quarterly Report on
                   Form 10-Q for the quarter ended September 30, 1998,
                   in File No. 1-3480.

     *4(c)         Rights Agreement, dated as of November 12, 1998,
                   between the Company and Norwest Bank Minnesota,
                   N.A., filed as Exhibit 4.1 to Form 8-A on November 12,
                   1998, in File No. 1-3480.

      5(a)         Opinion of Lester H. Loble, II, Esq., General Counsel to
                   the Company.

      5(b)         Opinion of LeBoeuf, Lamb, Greene & MacRae, L.L.P.,
                   counsel to the Company.

     23(a)         Consent of Arthur Andersen LLP.

     23(b)         Consent of Lester H. Loble, II, Esq. (contained in
                   opinion filed as Exhibit 5(a) hereto).

     23(c)         Consent of LeBoeuf, Lamb, Greene & MacRae, L.L.P.
                   (contained in opinion filed as Exhibit 5(b) hereto).

- ----------
*Incorporated herein by reference as indicated.

                                      II-5