We investigate role of atP sensitive potassium (KatP) channel in cytotoxic effect of cypermethrin on rataortic smooth muscle cells. cytotoxicity analysis was performed at 0, 0.1, 0.5, 10, 50, and 100 µMconcentrations of cypermethrin and the cell index (ci) was calculated. KatP currents were recorded usingpatch clamp technique for 50 and 100 µM concentrations and channel conductivity was determined byobtaining current-voltage characteristics. No cytotoxic effect was observed in the first 72 hours. at the96th hour, only at 100 µM concentration, the ci value decreased significantly compared to control groupand at 120 and 144th hours, it was observed that the ci value decreased significantly at all concentrations.currents and conductivities were significantly decreased at 50 and 100 µM concentrations. Results gaveclues that cypermethrin causes a cytotoxic effect on vascular smooth muscles and that KatP channelsmay have a role in the emergence of this effect.