Phosphatases are important enzymes in a variety of biochemical pathways in different cells which they catalyze opposing reactions of phosphorylation and dephosphorylation, which may modulate the function of crucial signaling proteins in different cells. This is an important mechanism in the regulation of intracellular signal transduction pathways in many cells. Phosphatases play a key role in regulating signal transduction. It is known that phosphatases are specific for cleavage of either serine-threonine or tyrosine phosphate groups. To date, numerous compounds have been identified. This paper reviews the classification, roles and pharmacological of protein serine/threonine phosphates.