Antitumor activity of Sarcodon aspratus (Berk.) S. Ito and Ganoderma lucidum (Fr.) Karst. was investigated. Methanol and aqueous extracts of these Japanese mushrooms were tested for antitumor activity against solid type of sarcoma 180 by intraperitoneal or oral administration. The aqueous extract was remarkably effective for inhibition of tumor growth, but the methanol extract was not. The fraction of molecular weight more than 10000 had a high inhibitory activity against the tumor growth, but the fraction of molecular weight less than 10000 did not. Fractionation was carried out by using an ion-exchanger, and fraction S-4 having the highest carbohydrate content had the highest antitumor activity by intraperitoneal administration.