Gamma irradiation is used as a sterilization method for joint prosthesis. For this procedure, gamma irradiation causes crosslinking of UHMWPE. Crosslinked UHMWPE molecules connect each other strongly. However gamma irradiation causes the reduction in mechanical properties such as tensile strength and elongation because primary chain scission occurrs. Therefore, excessive irradiation would cause some problems. We suggest the existence of the optimum dose for minimum wear and moderate reduction in tensile strength and elongation. Furthermore we indicate a mechanism of wear resistance of gamma irradiated UHMWPE.