Carbon fibers (CF) were surface treated with air-oxidation and rare earth solution (RES), respectively. The friction and wear properties of the polyimide (PI) composites filled with differently surface-treated carbon fibers (20 vol.%), sliding against GCr15 steel under oil-lubricated condition, were investigated on a ball-on-block reciprocating UMT-2MT tribometer. Experimental results revealed that RES treatment largely reduced the friction and wear of CF reinforced PI (CF/PI) composites. Scanning electron microscope (SEM) investigation of worn surfaces of CF/PI composites showed that RES treated CF/PI composite had the strongest interfacial adhesion and the smoothest worn surface under given load and reciprocating sliding frequency. X-ray photoelectron spectroscopy (XPS) study of carbon fiber surface showed that the oxygen concentration was obviously increased after RES treatment. The increase in the amount of organic functional groups increased the interfacial adhesion between CF and PI matrix, and accordingly lowered coefficients of friction and wear rates. (C) 2007 Elsevier B.V. All rights reserved.