Friction and wear behavior of ultra-high molecular weight polyethylene (UHMWPE) sliding against Al2O3 ceramic under dry sliding,and lubrication of fresh plasma, distilled water and physiological saline were investigated with a self-made pin-on-disk apparatus at37±1℃. The worn surfaces were examined with a scanning electron microscope (SEM). The results show that the friction behavior ofUHMWPE is very sensitive to its water absorption state. The wear rate of UHMWPE under dry sliding is the highest and under plasmalubrication is the lowest. The wear mechanisms are different under dry friction and various lubricating conditions.