A strongly cytotoxic fraction (Fc-2, ED50=0.0003$mu extrm{g}$/ml) against L1210 cell was obtained from the root, seed and fruit of Trichosanthes kirilowii. Administration of Fc-2 prolonged the life span of the BDF1 mice bearing L1210 and the ICR mice bearing S-180 by 135%, and 130%, respectively. The Fc-2 affected L1210 cells were enlarged in their diameters two or three times in comparison with the untreated ones. When 20mg/kg of Fc-2 was administered, intraperitoneally, all the mice were killed.