Wear is the primary cause of failure of joint replacement prostheses. In this paper, the Ultra High Molecular Weight Polyethylene (UHMWPE) as an artificial joint acetabular material was reinforce by nano-ZrO2 particles. The friction and wear properties of ZrO2 - UHMWPE composites sliding against the Co-Cr-Mo alloy were studied under lubrication of distilled water, saline and calf serum. The worn surface is observed by the optics microscope to examine the wear mechanism of the composite. The hardness and wetting angle of the composites were also measured. The result shows that the hardness, wettability, friction and wear resistance were all improved by filing with nano-ZrO2 particles. The 2%ZrO2 - UHMWPE composite had the lowest wear rate.