The gamma radiation induced graft copolymerization of 2, 2, 6, 6-tetramethyl-4-piperidinyl-methacrylate (TMPM) ,a very effective hindered amine light stabilizer (HALS) ,onto polypropylene was investigated by simultaneous-irradiation technique. The effects of various synthesis conditions on the graft content were studied. It was shown that percent grafting in benzene,CCl,4, and petroleum ether were higher than that in other solvents. The percent grafting was higher when graft copolymerization was carried out in argon atmosphere than that in air. For the grafting copolymerization carried out in benzene,percent grafting increased linearly from 10 to 60 kGy and beyond 60 kGy a tendency to level off was appeared. In CCl,4, percent grafting increased linearly from 10 to 50 kGy and beyond 50 kGy a tendency to level off was appeared. Percent grafting also increased continuously with increasing monomer concentration up to 2.85mol/L, but significant increase was observed only up to 1.14 mol/L. The percent grafting decreased when inhibitor was used,the difference of percent grafting between the samples with and without inhibitor became smaller with the increase of irradiation dose. The stabilizing effectiveness of grafted TMPM on the radiation resistance of Polypropylene was found to be better than that of TMPM monomer.