The antitumor activity of berberine, berberrubine, and their derivatives against sarcoma-180 ascites was determined by the total packed cell volume method. Berbine and tetrahydroberberine derivatives had no antitumor activity, but berberrubine (9-demethylberberine) and the ester derivatives of berberrubine had a strong antitumor activity. ED90 of berberrubine, its acetate and benzoate, were 15, 23, and 44 mg/kg, respectively. The therapeutic indices (LD10/ED90 by the present method) of these compounds were as follows: Berberrubine hydrochloride, 6.7 approximately 9.4; 9-acetyl-9-demethylberberine (9-acetylberberrubine) chloride, 7.6 approximately 8.7; 9-benzoyl-9-demethylberberine (9-benzoylberberrubine) chloride, 3.4 approximately 4.9.