Abstract: The friction and wear properties of Ultra-high-molecular-weight-polyethylene (UHMWPE) and its composites filled with nanocrystalline Al 2O 3 were investigated with an MM-200 friction and wear tester, with an emphasis on exploring the effect of load and the counterpart surface roughness (grit size of blast SiC) on the tribological behavior. The worn surfaces of UHMWPE and its composites were examined with a scanning electron microscope, as an attempt to examine the wear mechanism of the composites. It has been found that the addition of nanocrystalline Al 2O 3 increases the hardness, wear resistance, and the friction coefficient of UHMWPE in sliding against steel with or without blast SiC coating. Increased wear mass losses of UHMWPE and its composites are observed with increasing grit size of the blast SiC coating on the counterpart surface. UHMWPE and its composites are characterized by plastic deformation and abrasive wear in sliding against the SiC-blast-coating steel ring.