The graft terpolymer of methacrylonitrile (MAN) and 2-vinylnaphthalene (2-VN) onto ethylene-propylene-diene terpolymer (EPDM) was synthesized in toluene using benzoyl peroxide (BPO) as an initiator. The effects of EPDM content, mole ratio of 2-VN to MAN, reaction time, reaction temperature, and initiator concentration on the graft copolymerization were examined. The synthesized graft terpolymer was identified by IR and H-1-NMR spectroscopies. The light resistance, thermal stability, molecular weight, and tensile properties of the graft terpolymer were investigated by Fade-o-meter, thermogravimetric analysis, gel permeation chromatography (GPC), and a universal tensile machine (UTM). It was found that the light resistance and heat resistance as well as-the tensile strength of the graft terpolymer are considerably better than those of the acrylonitrile-butadiene-styrene(ABS) terpolymer.