The effects of oral administration of cryomilled powder of the soft-shelled turtle (SST powder) on solid and ascites tumor-bearing C3H/He mice were studied. The SST powder was administered orally at a dose of 100 or 500mg/kg/d for two or four weeks, and then MH134 hepatoma cells were inoculated; oral administration was continued after inoculation. Treatment with the SST powder attenuated the increase in diameter and weight of the tumor and prolonged the survival of mice with solid tumors. However, the same treatment did not show any significant effect in mice with ascites tumor, indicating that the SST powder has no direct killing action on tumor cells. These results suggest that oral administration of the SST powder decreases the growth of solid tumors possibly by activating the host immune system.