Protein phosphorylation and dephosphorylation are major regulatory mechanisms that cells use to transmit signals from their extracellular environment to the interior. Up to now, two structurally distinct groups of ser/thr phosphatases are known of: the PP1/PP2A family and the PP2C family. Here, we focus our efforts to reveal the functions of the PP2C family in rice. It has been known that PP2C has diverse functions related to developments and stress responses. We have obtained a rice EST clone, OsPP2C4, that contained the highly conserved PP2C motifs. RNA gelblot analysis showed that OsPP2C4 was expressed highly in panicles, while it was expressed weakly in seedling leaves, seedling roots, and mature leaves. Assay of the PP2C enzyme activity with a substrate, para-nitrophenyl phosphate, showed that 05PP2C4 encoded an active PP2C. Transgenic plants expressing the antisense construct of this clone were generated to study the functional roles of the PP2C clone in rice.