AIM: To characterize the electrophysiological and kinetic properties of Ca2+-activated chloride channel (CaCC) in cultured human umbilical vein endothelial cell line (HUVEC), and test the inhibitory effects of tetrandrine (Tet) on CaCC. METHODS: Ca2+-activated Cl- currents (ICl,Ca) were recorded by patch-clamp whole cell configurations.[Ca2+]i was measured via intracellular Fura-2 fluorescence intensities. RESULTS: ICl,Ca was activated by increasing [Ca2+]i via direct elevation of intracellular calcium. ICl,Ca showed an apparent outward rectification properties, and it was activated in a voltage- and calcium-dependent mode. Tet dose-dependently inhibited ICl,Ca, the IC50 was (5.2±0.4)μmol/L (n=8 cells). Tet suppressed both voltage-dependent and calcium-dependent activation of ICl,Ca. The activation time constant was (326± 12) ms [in the presence of 10 μmol/L Tet, compared to control (175± 17) ms, at +100 mV], and Ca2+ concentration for half maximal activation was (387±61) nmol/L for Tet (compared to control (287±36)nmol/L. CONCLUSIONS: Tet effectively blocked ICl,Ca, and such effects might be due to its inhibitory effects on the activation process of Ca2+-activated chloride channel.