Abstract The importance of protein phosphatases in eukaryotic cell cycle control was only recently established. Mutations in both protein tyrosine and serine/threonine phosphatase genes display distinct cell cycle phenotypes. Classes of phosphatases identified in fission yeast are described in regard to their positive and negative roles in the regulation of cell division cycle. Type 2A-like ppa2 and type 1-like dis2 phosphatases play vital roles in the regulation of mitotic entry and exit. The negative regulation of mitotic entry by ppa2 phosphatase, which is the in vivo target of okadaic acid, is discussed. An intermediate class phosphatase ppe 1 controls cell shape and is implicated in mitotic control. A phosphatase regulator, sds22, which directly interacts with the dis2 catalytic subunit and controls the midmitotic progression, is identified and its role in mitosis discussed.