Antitumor activities of gallic acid, pyrogallol, phloroglucinol, protocatechuic acid, vanillin, guiacol, pyrocatechol and resorcinol were investigated with NF sarcoma and sarcoma 180. Among these phenols, pyrocatechol and guiacol showed the highest effect. Resorcinol and protocatechuic acid were not so active as these two. The rest of them scarcely had the action. Dihydroxyphenylalanine (DOPA) and adrenalin, which are normal components in mammals also had the anticancer potency. It was observed that an intimate relation exists between antitumor activities of phenols and their oxidation potentials.