Carbon fibers (CFs) were treated by HNO3 plus diamine modification and incorporated into polyimide (PI) matrix to prepare polymer composites. The friction and wear properties of the PI composites reinforced by untreated and treated carbon fibers (15 wt.%), sliding against GCr15 steel, were studied on an M-2000 model ring-on-block test rig under dry sliding. Experimental results showed that the surface treatment largely reduced the friction and wear of CFs reinforced PI (CFs/PI) composites. The worn surface of CFs/PI composites and the transfer films formed on the surface of the counterpart ring sliding against CFs/PI composites were investigated by SEM. Compared with the untreated ones, the surface modified CFs can enhance the tribological properties of CFs/PI composite efficiently due to the improved adhesion between Us and PI matrix. The differences in the friction and wear properties of CFs/PI composites are closely related with the sliding condition such as sliding rate and the applied load. Research results show that CFs/PI composites exhibited better tribological properties under higher load and sliding speed. (C) 2009 Elsevier B.V. All rights reserved.