Abstract: Cryptolepisin is a cardiac glycoside isolated from the roots of Cryptolepis buchanani Roem. et Schult., which was collected in the subtropical zones of Yunnan. It gave positive reactions with Legal and Keller-Kiliani tests. Cryptolepisin produced a systolic standstill in frog heart in situ. On urethanized rabbits, an i.v. dose of 6 mg/kg increased the amplitude of heart contractions, decreased the rate, and finally stopped the heart in systole. When the isolated guinea pig heart was perfused, cryptolepisin in concentrations 1.5×10^-5 or 3.0×10^-5 induced successive positive inotropic action and final stoppage of the heart in systole. It induced in guinea pigs ECG changes similar to those induced by digitalis. It caused vomiting in pigeons. The minimum lethal dose of cryptolepisin in pigeons were found to be 2.914±0.037 mg/kg, while that of adonidine was 2.829±0.023. By testing in pigeons, the accumulation rate of cryptolepisin was found to be 32.5% at the end of 24 hours after administration.