If a large amount of polymer radicals remain trapped after the irradiation of ultrahigh molecular weight polyethylene (UHMWPE), the radicals may result in a significant alteration of its physical properties during long-term shelf storage and implantation. An electron spin resonance spectroscopic study was undertaken to investigate the remaining free radicals in UHMWPE after electron beam irradiation tip to 500 kGy in air and an N-2 environment. Heat treatment was employed at 110 and 145° C for various periods of time to decay the free radicals. The free radicals were rapidly decayed for 1h and gradually decayed as a function of lime with the heat treatment. The decay of the free radicals was completed more rapidly with a heat treatment at 145° C than at 110° C. Therefore, a longer heat treatment time is required to scavenge all the free radicals formed in UHMWPE at 110° C. The oxidation profiles showed that the oxidation index of the heat-treated UHMWPE was lower than the oxidation index of the non-heat-treated UHMWPE. The heat treatment of irradiated UHMWPE can substantially reduce the concentration of free radicals; therefore, UHMWPE has resistance against long-term oxidative degradation. © 2005 Wiley, Periodicals, Inc.