To find antitumor components with low toxicity in natural products of Korean Basidiomycete, the carpophores of Flammulina velutipes (Fr.) Sing. were extracted with hot water for eight hours. The extract was purified by dialyzing through Visking tube and a protein-bound polysaccharide fraction was obtained as pale brownish amorphous powder after it was freeze-dried. The fraction was examined for antitumor activity against sarcoma 180 implanted subcutaneously in the left groins of I.C.R. mice. The inhibition ratio of this fraction of against the tumor was 62.3% at the dose of 10 mg/kg/day for the period of ten days. The tumors in three of the ten treated mice were completely regressed.