Abstract: The coordinated regulation of contraction is a key property of smooth muscle，Proper function contributes to general health，but dysfunction is associated with morbidity and mortality.CPI-17（protein kinase C-potentiated phosphatase inhibitor of 17 ku）is a phosphorylation-dependent myosin phosphatase inhibitory protein，increases the phosphorylation level of 20 ku myosin light chain and enhances smooth muscle contraction.Multiple kinases and phosphateses are involved in regulating CPI-17 phosphorylation.Recent evidences show that up-and down-regulation of CPI-17 occurs under pathophysiological conditions，resulting in abnormal contraction of various smooth muscle，such as myometrium，blood vessel，trachea，gastrointestinal tract.Further studies on regulatory mechanism of CPI-17 on smooth muscle will be useful to elucidate the pathogenesis of many diseases/disorders associated with smooth muscle dysfunction and provide a new idea for the clinical treatment.

Key words: Protein phosphatase 2, Myosin-light-chain phosphatase, Myocytes, smooth muscle, Calmodulin-binding proteins, CPI-17