The styrene-EPDM-vinylacetate (SEV) graft polymer, which linked respectively the styrene (St) unit and vinylacetate the (VAc) unit to the ethylene-propylene-diene terpolymer (EPDM) backbone was synthesized by two-step graft polymerizations: First the graft polymerization of VAc onto EPDM was carried out, and then St was added successively in the prepolymerized solution and further polymerized for a given period to obtain SEV. The effects of concentration of EPDM and an initiator, mole ratio of VAc to St, polymerization time, temperature, and solvent were examined on the graft polymerizations. The synthesized graft polymers (SEVs) that have different contents of St or VAc were identified by Fourier transform IR spectrum. The highest graft ratio has been obtained by 10 wt % of EPDM, 1.0 mole ratio of VAc to St, and 1.0 wt % of BPO in toluene for 48 h at 70 degrees C. The glass transition temperature of SEV is lower than that of poly(vinyl acetate) (PVAc) and polystyrene (PS). The thermal stability of SEV is higher than that of PVAc, PS, and the acrylonitrile-butadiene-styrene (ABS) resin. The tensile strength of SEV was improved as compared with that of EPDM. The light resistance and weatherability of SEV were better than those of ABS.