Ultra-high molecular weight polyethylene (UHMWPE) has been used for the bearing materials of total joint prostheses. Strength criterion of medical UHMWPE is the tensile properties. However, the compression characteristic which is important in the contact surfaces of the prosthesis has not been considered. In this study, we examined the effect of gamma and electron beam irradiation treatment on compressive properties of medical UHMWPE. The compressive properties (Young's modulus and proof stress) by γ irradiation was higher than the specimens of unirradiated. The plastic flow pressure by electron beam irradiation showed higher than the specimens of unirradiated. Inhibition of plastic deformation of the non-crystalline structure part by electron beam irradiation is considered to have caused the increase in the plastic flow pressure. Electron beam irradiation treatment was found to be effective for the surface enhancements of the medical UHMWPE. ESR signal was clearly observed in the irradiated UHMWPE. From these results, it was found that there was a high possibility that dangling bonds were formed in the irradiated UHMWPE.