The radiation-induced graft copolymerization of vinyl acetate (VAc) onto ethylene-co-propylene rubber (EPR) has been studied in methanol with radiation of cobalt-60. The effects of irradiation dose, dose rate, concentration of monomer, Cu++ concentration, and temperature on the degree of grafting were investigated. The dependence of the initial grafting rate on dose rate, monome, and Cu++ concentration were found to be 1.0, 1.95, and 0.5 order, respectively. The apparent activation energy was calculated to be 49 kJ/mol. Mechanical properties of the grafted polymer were investigated as a function of the grafting percentage. The tensile strength increases and elongation of break decreases with the increase of the degree of grafting in the region of low grafting percentage (congruent to 10%).