<PAGE>   1
                                                                      Exhibit 24


                                 OM Group, Inc.

                                    Form 10-K
                        Power of Attorney for Directors

The undersigned, a director of OM Group, Inc., a Delaware corporation (the
"Company"), which anticipates the filing with the Securities and Exchange
Commission (the "Commission") under the provisions of the Securities Exchange
Act of 1934 (the "Act") a Form 10-K (together with any and all subsequent
amendments, the "Form 10-K"), does hereby constitute and appoint James P.
Mooney, James M. Materna or Michael J. Scott and any one of them with full power
of substitution and resubstitution, as attorney or attorneys to execute and file
on behalf of the undersigned, in his capacity as director of the Company, the
Form 10-K and any and all other documents to be filed with the Commission
pertaining to the Form 10-K, with full power and authority to do and perform any
and all acts and things whatsoever required or necessary to be done in the
premises, as fully as to all intents and purposes a she could do if personally
present, hereby ratifying and approving the acts of said attorneys and any of
them and any such substitution.

Executed this 16th day of March 2001.

                                                     /s/ Edward W. Kissel


<PAGE>   2




                                 OM Group, Inc.

                                    Form 10-K
                         Power of Attorney for Directors

The undersigned, a director of OM Group, Inc., a Delaware corporation (the
"Company"), which anticipates the filing with the Securities and Exchange
Commission (the "Commission") under the provisions of the Securities Exchange
Act of 1934 (the "Act") a Form 10-K (together with any and all subsequent
amendments, the "Form 10-K"), does hereby constitute and appoint James P.
Mooney, James M. Materna or Michael J. Scott and any one of them with full power
of substitution and resubstitution, as attorney or attorneys to execute and file
on behalf of the undersigned, in his capacity as director of the Company, the
Form 10-K and any and all other documents to be filed with the Commission
pertaining to the Form 10-K, with full power and authority to do and perform any
and all acts and things whatsoever required or necessary to be done in the
premises, as fully as to all intents and purposes a she could do if personally
present, hereby ratifying and approving the acts of said attorneys and any of
them and any such substitution.

Executed this 16th day of March 2001.

                                                      /s/ Markku Toivanen



<PAGE>   3




                                 OM Group, Inc.

                                    Form 10-K
                         Power of Attorney for Directors

The undersigned, a director of OM Group, Inc., a Delaware corporation (the
"Company"), which anticipates the filing with the Securities and Exchange
Commission (the "Commission") under the provisions of the Securities Exchange
Act of 1934 (the "Act") a Form 10-K (together with any and all subsequent
amendments, the "Form 10-K"), does hereby constitute and appoint James P.
Mooney, James M. Materna or Michael J. Scott and any one of them with full power
of substitution and resubstitution, as attorney or attorneys to execute and file
on behalf of the undersigned, in his capacity as director of the Company, the
Form 10-K and any and all other documents to be filed with the Commission
pertaining to the Form 10-K, with full power and authority to do and perform any
and all acts and things whatsoever required or necessary to be done in the
premises, as fully as to all intents and purposes a she could do if personally
present, hereby ratifying and approving the acts of said attorneys and any of
them and any such substitution.

Executed this 16th day of March 2001.

                                                   /s/ Lee R. Brodeur



<PAGE>   4




                                 OM Group, Inc.

                                    Form 10-K
                         Power of Attorney for Directors

The undersigned, a director of OM Group, Inc., a Delaware corporation (the
"Company"), which anticipates the filing with the Securities and Exchange
Commission (the "Commission") under the provisions of the Securities Exchange
Act of 1934 (the "Act") a Form 10-K (together with any and all subsequent
amendments, the "Form 10-K"), does hereby constitute and appoint James P.
Mooney, James M. Materna or Michael J. Scott and any one of them with full power
of substitution and resubstitution, as attorney or attorneys to execute and file
on behalf of the undersigned, in his capacity as director of the Company, the
Form 10-K and any and all other documents to be filed with the Commission
pertaining to the Form 10-K, with full power and authority to do and perform any
and all acts and things whatsoever required or necessary to be done in the
premises, as fully as to all intents and purposes a she could do if personally
present, hereby ratifying and approving the acts of said attorneys and any of
them and any such substitution.

Executed this 16th day of March 2001.

                                             /s/ Thomas R. Miklich




<PAGE>   5




                                 OM Group, Inc.

                                    Form 10-K
                         Power of Attorney for Directors

The undersigned, a director of OM Group, Inc., a Delaware corporation (the
"Company"), which anticipates the filing with the Securities and Exchange
Commission (the "Commission") under the provisions of the Securities Exchange
Act of 1934 (the "Act") a Form 10-K (together with any and all subsequent
amendments, the "Form 10-K"), does hereby constitute and appoint James P.
Mooney, James M. Materna or Michael J. Scott and any one of them with full power
of substitution and resubstitution, as attorney or attorneys to execute and file
on behalf of the undersigned, in his capacity as director of the Company, the
Form 10-K and any and all other documents to be filed with the Commission
pertaining to the Form 10-K, with full power and authority to do and perform any
and all acts and things whatsoever required or necessary to be done in the
premises, as fully as to all intents and purposes a she could do if personally
present, hereby ratifying and approving the acts of said attorneys and any of
them and any such substitution.

Executed this 16th day of March 2001.

                                                  /s/ John E. Mooney





<PAGE>   6




                                 OM Group, Inc.

                                    Form 10-K
                         Power of Attorney for Directors

The undersigned, a director of OM Group, Inc., a Delaware corporation (the
"Company"), which anticipates the filing with the Securities and Exchange
Commission (the "Commission") under the provisions of the Securities Exchange
Act of 1934 (the "Act") a Form 10-K (together with any and all subsequent
amendments, the "Form 10-K"), does hereby constitute and appoint James P.
Mooney, James M. Materna or Michael J. Scott and any one of them with full power
of substitution and resubstitution, as attorney or attorneys to execute and file
on behalf of the undersigned, in his capacity as director of the Company, the
Form 10-K and any and all other documents to be filed with the Commission
pertaining to the Form 10-K, with full power and authority to do and perform any
and all acts and things whatsoever required or necessary to be done in the
premises, as fully as to all intents and purposes a she could do if personally
present, hereby ratifying and approving the acts of said attorneys and any of
them and any such substitution.

Executed this 16th day of March 2001.

                                                 /s/ Frank Butler





<PAGE>   7




                                 OM Group, Inc.

                                    Form 10-K
                               Power of Attorney

The undersigned, Chief Financial Officer of OM Group, Inc., a Delaware
corporation (the "Company"), which anticipates the filing with the Securities
and Exchange Commission (the "Commission") under the provisions of the
Securities Exchange Act of 1934 (the "Act") a Form 10-K (together with any and
all subsequent amendments, the "Form 10-K"), does hereby constitute and appoint
James P. Mooney, James M. Materna or Michael J. Scott and any one of them with
full power of substitution and resubstitution, as attorney or attorneys to
execute and file on behalf of the undersigned, in his capacity as director of
the Company, the Form 10-K and any and all other documents to be filed with the
Commission pertaining to the Form 10-K, with full power and authority to do and
perform any and all acts and things whatsoever required or necessary to be done
in the premises, as fully as to all intents and purposes a she could do if
personally present, hereby ratifying and approving the acts of said attorneys
and any of them and any such substitution.

Executed this 16th day of March 2001.

                                                 /s/ James M. Materna