The technique of ion implantation was employed for improving surface hardness and wear resistance of Polyphenylene Oxide(PPO). The samples of PPO were implanted separately with Al, Ti and Fe ions to three doses of 2×1015 ions cm－2, 1×1016 ions cm－2 and 1×1017 ions cm－2. Nano-hardness increased from 0.369 GPa for the plain PPO to 1.433 GPa for 1×1016 ions cm－2 Ti-implanted PPO. The cross-linking structures induced by ion implantation were responsible for the improvements in hardness. Wear tests showed that wear-resistance of PPO was improved significantly and friction coefficient was reduced. 1×1016 ions cm－2 Ti ion implantation produced the largest improvement in tribological properties, and wear volume and friction coefficient of 1×1016 ions cm－2 Ti-implanted PPO were reduced respectively to 0.4% and 60% as compared to those of the pristine PPO. IR spectra of Al and Ti-implanted PPO indicated the occurrence of the hydroxyl and carbonyl groups on the implanted PPO surface. The formation of the hydroxyl group was related to moisture absorption on the sensitized PPO surface after the specimens were exposed to the atmosphere. Electron Spin Resonance (ESR) analyses showed that ion implantation could lead to the formation of free radicals and the main cross-linking mode was the reactions among the free radicals.