It has been found that nano- or microsized inorganic particles in general enhance the tribological properties of polymer materials. In the present study, 5 vol % nano-TiO2 or micro-CaSiO3 was introduced into a polyetherimide (PEI) matrix composite, which was filled additionally with short carbon fibers (SCF) and graphite flakes. The influence of these inorganic particles on the sliding behavior was investigated with a pin-on-disc testing rig at room temperature and 150 degrees C. Experimental results showed that both particles could reduce the wear rate and the frictional coefficient (mu) of the PEI composites under the applied testing conditions. At room temperature, the microparticles-filled composites exhibited a lower wear rate and mu, while the nano-TiO2-filled composites possessed the lowest wear rate and mu at elevated temperature. Enhancement in tribological properties with the addition of the nano-particles was attributed to the formation of transfer layers on both sliding surfaces together with the reinforcing effect. (c) 2006 Wiley Periodicals, Inc.