Abstract: The friction and wear properties of UHMWPE and its composite filled with carbon black sliding against AISI-1045 steel in a block-on-ring configuration were investigated on an MM-200 friction and wear tester, with the effect of load and counterpart surface roughness on the tribological behavior to be focused on. The worn surfaces of UHMWPE and its composite were examined on a scanning electron microscope (SEM). It was found that the addition of the carbon black contributed to increase the wear resistance of UHMWPE, which was attributed to the load-carrying action of the carbon black particulates as the filler. The counterpart surface roughness had a great influence on the tribological behavior of the carbon black filled UHMWPE composite, and the wear mass loss of the composite considerably increased with increasing load and counterpart surface roughness as well, which was attributed to the enhanced ploughing and cutting action of the hard asperities on the counterpart surface of a larger surface roughness at increased normal load. UHMWPE and carbon black filled UHMWPE composite were characterized by ploughing and plastic deformation as they slid against the steel counterpart under unlubricated condition. The incorporation of the carbon black contributed to abate the ploughing and plastic deformation of the filled composite, which conformed to the better wear-resistance of the filled composite than the polymer matrix.