Mimasaka (美作国 -no kuni) or Sakushu (作州 sakushū) was a province of Japan in the part of Honshu that is today northeastern Okayama Prefecture. Mimasaka bordered Bitchu, Bizen, Harima, Hoki, and Inaba Provinces.

Mimasaka was landlocked, and was often ruled by the daimyo in Bizen. The ancient capital and castle town was Tsuyama.