Abstract: Objective To investigate the effects of Urotensin II（UII）on the proliferation of rat pheochromocytoma cell line (PC12) and human pheochromocytoma cells primary cultured .Methods We observed the effects of UII on the proliferation of rat PC12 cells and human pheochromocytoma cells primary cultured in vitro by MTT method. Results 1. UII had no obvious effect on the proliferation of rat PC12 cells.2. UII (at 10-7 and 10-6M) promote the proliferation of human pheochromocytoma cells in the primary culture. Conclusions UII stimulates the proliferation of human pheochromocytoma cells and it probably play a role in the pathogenesis of pheochromocytoma.