The surface of ultra high molecular weight polyethylene (UHMWPE) was exposed to gamma-ray for improving bonding strength to polymethylmethacrylate (PMMA) bone cement. Two types of irradiation methods, pre-irradiation and syn-irradiation, were engaged in this study. The intensity of irradiation was 5-30 kGy for pre-irradiation, and 1-3 kGy for syn-irradiation. The grafting process was performed in a glass ampule filled with methanol, MMA monomer (60 v%), FeSO4 center dot 7H(2)O (1.5 x 10(-4) M) and H2SO4 (0.1 M). The graft rate of each specimen was measured with time variation. The grafting effect of the acrylates on to the UHMWPE surface was investigated by mechanical test for bonding strength. Pre-irradiation method showed thinner coverage PMMA graft on the surface of the UHMWPE and higher bonding strength than syn-irradiation method. The interfacial bonding strength between UHMWPE and PMMA bone cement was considerably improved by gamma-ray irradiation method. For medical application, the pre-irradiation method might be recommended, because the PMMA could be grafted as optimized thickness to the UHMWPE surface. (c) 2005 Elsevier B.V. All rights reserved.