The graft polymerizations of N-isopropylacrylamide (NIPAM) or N-phenyl-acrylamide (NPAM) onto ethylene-propylene-diene terpolymer (EPDM) were carried out with benzoyl peroxide (BPO) as an initiator in toluene or THF. The structures of synthesized graft polymers, EPDM-g-N-isopropylacrylamide (ENIPAM) and EPDM-g-N-phenylacrylamide (ENPAM), were identified by infrared (IR) spectroscopy. The effects of monomer concentration, reaction time, and initiator concentration were investigated on the graft polymerization. The highest graft efficiency of NIPAM was obtained at 0.75 mol/L of NIPAM, 4 g of EPDM, 3 wt % of BPO, and 70 degrees C for 48 h and that of NPAM did not much change up to 0.75 mol/L of NPAM, 4 g of EPDM, 3 wt % of BPO, and 70 degrees C for 72 h. The thermal decomposition temperatures, wettabilities, and tensile strengths of ENIPAM and ENPAM all decreased with an increasing concentration of NIPAM and NPAM moiety in the corresponding polymers, respectively. The morphologies of ENIPAM and ENPAM after irradiation showed many gel particles as compared with those of ENIPAM and ENPAM before irradiation. The UV light and Co-60 gamma-ray resistances of ENIPAM and ENPAM were worse than those of EPDM due to carbonyl group in NIPAM and NPAM.