Abstract: The effects of benzyltetrahydropalmatine(BTHP)on delayed rectified K⁺ currents(I_k)expressed in Xenopus cocytes and I_k of toad(Bufo bufo gargarizans)cocytes were studied.The I_k expressed in Xenopus oocytes was measured after microinjection of mRNA isolated from carp fish(Canratus L.)brains with double-microelectrode voltage clamp technique.The maximum and meanvalue of I_k expressed in Xenopus oocytes were 600 nA and 360±104 nA,respectively.BTHP reducedthe current amplitude of I_k expressed in Xenopus cocytes in 10～1000 μmol·L^-1 dose-dependently,EC₅₀ was 29μmol·L^-1.Also,the reduction of I_k of toad oocytes was 9.1%,29.1%,54.7% and68.6% by BTHP 10,30,100 and 1000μmol·L^-1,respectively,EC₅₀ was 33μmol·L^-1,The results showed that BTHP possesses an inhibitory effect on I_k,the main ion mechanism ofantiarrhythmic action of BTHP.