A graft copolymer of 2-vinylnaphthalene (2-VN) and methyl methacrylate (MMA) onto ethylene-propylene-diene terpolymer (EPDM) was synthesized in tetrahydrofuran using benzoyl peroxide. The effects of EPDM content, mol ratio of 2-VN to MMA, reaction time, reaction temperature, and initiator concentration in the graft copolymerization were examined. The light resistance, thermal stability, and the tensile properties of the graft copolymer were investigated by using Fade-o-Meter, thermogravimetric analyzer, and tensile tester. It was found that the light resistance and the heat resistance as well as the tensile strength of the graft copolymer are considerably better than those of the acrylonitrile-butadiene-styrene (ABS) copolymer.