Anti-tumor activity of oral administration of 1-Acetyl-3-o-toluyl-5-fluorouracil at a dose of 0.2 mmol/kg/d is comparable to that of subcutaneous administration of 5-fluorouracil at the same dose. The level of decrease in thymus weight and the magnitude of increase of spleen weight following oral administration of 1-Acetyl-3-o-toluyl-5-fluorouracil at any dose are smaller than those by subcutaneous administration of 5-fluorouracil (0.2 mmol/kg/d).