Polyimide composites reinforced with shortcut fibers such as carbon, glass, and quartz fibers were fabricated by the polymerization of monomer reactants process. The mechanical properties of the composites with different fiber contents were evaluated. The friction and wear properties of the polyimide and its composites were investigated under dry-sliding and water-lubricated conditions. The results indicated that the short-carbon-fiber-reinforced polyimide composites had better tensile and flexural strengths and improved tribological properties in comparison with glass-fiber- and quartz-fiber-reinforced polyimide composites. The incorporation of short carbon fibers into the polyimide contributed to decreases in the friction coefficient and wear rate under both dry and water-lubricated conditions and especially under water lubrication because of the boundary lubrication effect of water. The polyimide and its composites were characterized by plastic deformation, microcracking, and spalling under both dry and water-lubricated conditions, which were significantly abated under the water-lubricated condition. The glass and quartz fibers were easily abraded and broken; the broken fibers transferred to the mating metal surface and increased the surface roughness of mating stainless steel, which led to the wear rate increasing for the glass-fiber- and quartz-fiber-reinforced polyimide composites. (C) 2007 Wiley Periodicals, Inc.