Abstract: A new substance having antitumor activity is obtained from an epidermal portion of rice. A substance called RBF-P is obtained by adding ethanol to an aqueous alkaline extract of rice bran, removing the insolubles and precipitating the substance by addition of an acid. This substance comprises an active substance called RBF-PM, which is insoluble in methanol, and an active substance called RBF-X, which is soluble in acetone. The substance RBF-PM is a protein containing extremely little cystine and said protein can suppress solid cancers of mice. The substance RBF-X is a mixture of hexane-solubles such as fatty acids and a hexane-insoluble called RBF-H. A synergistic suppressive action on ascites hepatoma of mice is exhibited by the combination of the RBF-H and the fatty acids.