To find antitumor components with low toxicity in the Basidiomycetes of Korea, the carpophores of Flammulina velutipes (Fr.) Singer 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 freeze-drying. The fraction was examined for antitumor activity against sarcoma 180 implanted subcutaneously in the left groin in ICR mice. The inhibition ratio of this fraction against the tumor was 62.3% at the dose of 10mg/kg/day for the period of ten days. The tumors in three of the ten treated mice were completely regressed. The chemical analysis of the antitumor component by anthrone and Lowry-Folin methods showed that it consisted of a polysaccharide (42.4%) and a protein (24.5%). The hydrolysis of the polysaccharide moiety with 3% HCl-MeOH and trimethysilylation of the hydrolyzate yielded five monosaccharides which were identified by G.L.C. Several amino acids were identified by an amino acid autoanalyzer in the acid hydrolyzate of the protein moiety.