Objective: The aim of the present study was to study the effect of estrogen on the large-conductance Ca2+-activated potassium (BKCa) channel currents and spontaneous transient outward currents (STOCs) in mesenteric artery smooth muscle cells (SMCs) of post-menopoause hypertension female patients.The SMCs was isolated from the arteries using an enzymatic disassociation and the experimental groups were divided as premenopause women non-hypertension group (PNH), post-menopause women non-hypertension group (NH) and post-menopause women essential hypertension group (EH).Whole cell perforate patch technique was used to investigate the effect of estrogen and ICI 182780 (a specifc blocker of estrogen receptor) on BKCa in the SMCs and to explore the relation among estrogen, BKCa and women essential hypertension.The results showed: (1)The macroscopic currents of BKCa channels of women mesenteric SMCs had voltage-dependence and outward rectifying and the STOCs had voltage-dependence and randomness.(2) Estrogen (100 μmol/L) could activate the macroscopic currents of BKCa and the amplitude and frequency of STOCs in PNH group, NH group, EH group.ICI 182780 (100 μmol/L) could partly inhibit the action of estrogen on BKCa in no matter PNH or NH, EH groups.Compared with PNH group, the effect of estrogen on macroscopic currents and STOCs in NH was lower.The results suggested that estrogen play an important role in pre-menopause women.Compared with NH group, the effect of estrogen on macroscopic currents and STOCs in EH was lower.These data suggest that the responsiveness to estrogen was lower in mesenteric artery after hypertension and menopause was a factor of hypertension.(3)Estrogen could relax women mesenteric artery, and ICI 182780 could partly inhibit the effect, suggesting that BKCa and ER take part in the mechanisms of relaxing mesenteric artery by estrogen in human.