EX-99.906CERT

Green Century Funds
Exhibit 12(b) to Form N-CSR

                 CERTIFICATIONS PURSUANT TO SECTION 906 OF THE
                          SARBANES-OXLEY ACT OF 2002

I, Kristina A. Curtis, Chief Executive Officer of the Green Century Funds,
certify that, to my knowledge:

1. The Form N-CSR of the registrant (the "Report") fully complies with the
   requirements of Section 13(a) or 15(d) of the Securities Exchange Act of
   1934; and

2. The information contained in the Report fairly presents, in all material
   respects, the financial condition and results of operations of the
   registrant.

/s/ Kristina A. Curtis
- ------------------------------------
Kristina A. Curtis
President and Chief Executive Officer
April 10, 2007

A signed original of this written statement required by Section 906 of the
Sarbanes-Oxley Act of 2002 has been provided to the registrant and will be
retained by the registrant and furnished to the Securities and Exchange
Commission (the "Commission") or its staff upon request.

This certification is being furnished to the Commission solely pursuant to 18
U.S.C. (S) 1350 and is not being filed as part of the Form N-CSR with the
Commission.

I, Bernadette Buck, Treasurer and Chief Financial Officer of the Green Century
Funds, certify that, to my knowledge:

1. The Form N-CSR of the registrant (the "Report") fully complies with the
   requirements of Section 13(a) or 15(d) of the Securities Exchange Act of
   1934; and

2. The information contained in the Report fairly presents, in all material
   respects, the financial condition and results of operations of the
   registrant.

/s/ Bernadette L. Buck
- ------------------------------------
Bernadette L. Buck
Treasurer and Chief Financial Officer
April 10, 2007

A signed original of this written statement required by Section 906 of the
Sarbanes-Oxley Act of 2002 has been provided to the registrant and will be
retained by the registrant and furnished to the Securities and Exchange
Commission (the "Commission") or its staff upon request.

This certification is being furnished to the Commission solely pursuant to 18
U.S.C. (S) 1350 and is not being filed as part of the Form N-CSR with the
Commission.