PURPOSE: A mixture of at least one of polymerizable monomers and at least one of carcinostatic agents is irradiated with active rays to polymerize the monomers, thereby the combination remarkably improves the carcinostatic activity and the side- effect is reduced.

CONSTITUTION: A mixture consisting of 10 pts.wt. of at least one of polymerizable monomers, e.g., monomer glassifying at low temperatures, as hydroxyethyl methacrylate and 0.1W20 pts. of 2 or more kinds of carcinostatic agents as chloromethine, an alkylating agent or cytosyne arabinoside, an antimetabolite, or sarcomycin, an antibiotic, is irradiated with ionizing radiation to polymerize the monomers. The resulting polymer composition containing carcinostatic agents gradually liberates the active components at a controlled rate.