The effect of gamma irradiation and subsequent thermal treatment on the wear resistance and friction behavior of ultrahigh molecular weight polyethylene (UHMWPE) has been studied. Irradiation of the polymer was performed using a 60Co γ-emitter at laboratory temperature. Radiation dose 50 kGy was applied. Some irradiated samples were thermally treated at 150˚C for period of 30 min. and then slowly cooled to room temperature. A linear reciprocating tribometer was used to investigate the wear behavior of UHMWPE against Co-Cr-Mo alloy. The tests have been performed in unlubrication conditions. An important increase in wear resistance of the modified UHMWPE in comparison with the original material was proved. Besides wear rate the selected mechanical characteristics (friction coefficient, Young’s modulus, yield strength, fracture strength, and hardness) of original and modified samples of UHMWPE have been determined.