Air-oxidation and ozone surface treatment of carbon fibers (CF) on tribological properties of CF reinforced polytetrafluoroethylene (PTFE) composites under oil-lubricated conditions was investigated. Experimental results revealed that ozone treated CF reinforced PTFE (CF/PTFE) composite had the lowest friction coefficient and wear under various applied loads and sliding speeds compared with untreated and air-oxidated composites. X-ray photoelectron spectroscopy (XPS) study of the carbon fiber surface showed that, after ozone treatment, oxygen concentration was obviously increased, and the amount of oxygen-containing groups on CF surfaces were increased greatly. The increase in the amount of oxygen-containing groups enhanced interfacial adhesion between CF and PTFE matrix, and large scale rubbing-off of PTFE was prevented; therefore, the tribological properties of the composite were improved. (C) Koninklijke Brill NV, Leiden, 2010