Aim To investigate the characters of Ca 2+ -activated K + channels (KCa) of artery smooth muscle cell(SMC) from normal human mesentery. Methods Human normal mesenteric artery branch was digested by enzyme. Patch clamp technique was used to pull cell-attached and inside-out patches on the normal human mesenteric artery SMC respectively. The signal channel open and close times, open probability (P 0), open channel number per patch were recorded. Results The channels showed obviously voltage dependent, the amplitude voltagerelation curve can be linearly fitted during the voltage range from 10～60 mV(in symmetrical [K +] 0 140 mmol/L and [Ca 2+ ] free < 10 -9 mol/L). The KCa channels have slope conductance of 192.3±29.2 Ps and 202.5±58.3 Ps, in cell-attached and inside-out patches respectively. The channels were Ca 2+ sensitive . The single channel P 0 and open channel number per patch were increased apparently according to the increase of Ca 2+ (10 -8 ～10 6 mol/L) in cytoplasm . TEA in 2×10 -4 mmol applied in the out side of the channel can reduce the signal channel current amplitude. Conclusion The characters of KCa from normal human mesenteric artery SMC were mainly big conductance KCa, which have voltage and Ca 2+ concentration dependent and similar to other artery smooth muscle cell of human.