Ultra−high molecular weight polyethylene (UHMWPE) was irradiated in air by ,60,Co γ−rays. The effect of γ−ray irradiation on the structure and properties of UHMWPE was studied by FTIR, intrinsic viscosity measurement, melt flow rate (MFR) measurement and mechanical property test. The experimental results show that oxygen−containing groups (mainly carbonyl group) were introduced on the molecular chain of UHMWPE during the irradiation, which causeed degradation of UHMWPE. Molecular weight of UHMWPE decreased and melt flow rate increased obviously. Compared with the virgin UHMWPE, MFR of the 100kGy-irradiated UHMWPE increased from virtually nothing to 4.8g/10min. Tensile yield strength and elongation at break of the irradiated UHMWPE samples were improved, whereas notched Izod impact strength of the samples decreased. Compared with the virgin UHMWPE, elongation at break of the UHMWPE samples irradiated to 100kGy increased from 367% to 801%, and their notched Izod impact strength decreased to 576J/m from over 1000.