The graft copolymerization of monomer-olefins on polylpropylene film by a pre-irradiation of gamma-ray under atmosphere has been studied．Both radicals and peroxides，which were produced during the irradiation in air，can initiate graft copoly-merization．When the irradiated polymer is stored for a long period under atmosphere at 100℃ before grafting，the trapped radicals will decay gradually；although the grafting may be still induced by the peroxides，the degree of grafting is apparently decreased．The activation energy of the grafting initiated by the peroxide was calculated as 10.9—18.3 kcal／mol．Such grafted film may be dyed with direct or acid dyes in aqueous bath when the degree of graft is about 20％ by weight．It has been shown that the mechanical properties of the copolymer depend on its supramoleculer structures．