Poly(styrene-g-EVA) were prepared by irradiation of EVA-styrene mixture in air atmosphere. The mixtures (the solution of ELVAX 40 in styrene and the swollen ELVAX 250 in styrene) were irradiated in the cobalt 60 source at 15-20℃ with an average dose rage of 5.04×10⁴ mrad./hr. The grafted EVA were characterized in terms of % graft, with the dose, concentration and mixture phase as reaction variables. The results of grafting reactions indicated that the reactivity of the radicals formed at backbone and pendant acetate group (α-position) of EVA exhibited the similar reactivities toward monomer styrene. The dose rate doesn''t affect on the polymerization rate but only on the initial induction lag of grafting reactions. The dependence of % graft on concentration and mixture phase is negligible, and these phenomena are believed to be due to the fact that the occluded growing chains in viscous matrix attribute to the reaction more than the diffusion variable does on irradiation reactions. It appears that the grafting reaction kinetics of EVA-styrene system is similar to that of linear PE-styrene system''s.