Contracts for the two expire at the end of this season, and both have opted not to renew, Zap2it.com reported Tuesday. However, both are expected to make return appearances on the show next season.
"We think (the show) still has life in it," said Gail Berman, Fox Entertainment's president.
Berman said while the show's ratings slipped in the early part of the season, along with Fox as a whole, she expects them to bounce back some when "American Idol" and "The Simple Life" return to Wednesday nights in coming weeks.
Grace currently stars in the comedy "In Good Company," while Kutcher has a production company and several feature roles on tap.