A polysaccharide mixture was extracted from the mycelium of Coriolus versicolor with hot water and precipitated with ethanol. Fractionation with increasing concentrations of barium hydroxide solution and then with a cetyltrimethylammonium hydroxide solution afforded five fractions, among which a fraction precipitating with 0.3N barium hydroxide solution was found to have a marked antitumor activity against sarcoma-180 implanted in mice. This fraction was found to be composed of β-D-glucan and a smaller amount of protein, which could not be separated from the glucan moiety by any of the Sevag method, precipitation with trifluorotrichloroethane, digestion with pronase, or chromatography on a column packed with molecular sieves. On hydrolysis, this fraction gave D-glucose as the only carbohydrate component together with common amino acids. A β-glycosidic linkage was suggested from a low value of its specific optical rotation.