Abstract: In our experiments Chinese Catharanthus roseus Linn. G. Don was extracted with alcohol and 30 fractions were obtained. It was found that most of them possessed thera- peutic effect against Ehrlich ascites carcinoma in mice. AC-875 is a part of the total alkaloids; its antitumour action was proved to be higher than that of the other fractions. When AC-875 was administered intraperitoneally to mice and rats inoculated with ascites tumours such as Ehrlich ascites carcinoma, ascites hepatoma, and Yoshida ascites sarcoma, the survival times of the animals were prolonged significantly. AC-875 had no inhibitory action on other solid tumours. The acute LD₅₀ of AC-875 after an intraperitoneal injection to mice and rats was found to be 170 and 122mg/kg respectively. When AC-875 was injected intravenously to dogs in a daily dose of 2.5mg/kg for 10 days, the white cells counts were decreased but RBC, HB, liver and renal functions, urinalysis, and body weight remained normal.