The effects of addition of graphite(Gr)and nano ZnO on the tribological properties of polyimide(PI)composites against GCr15 steel were studied using a block on ring arrangement.The morphologies of the worn surface of PI composites and counterpart were observed with Scanning Electron Microscope.Experimental results reveal that single incorporation of Gr significantly improves the friction reducing and anti wear abilities of the PI composites.However,nano ZnO deteriorates the wear resistance of the PI composite drastically as single filler.A synergistic effect is found for the combination of nano ZnO and Gr,which leads to the best tribological properties.The friction and wear behaviors of the filled PI composites are closely related to the characteristics of their transfer film formed on the counterpart steel surface.Nano ZnO can improve the adhesion between the transfer film and the counterpart steel ring,and the different PI composites have different wear mechanism.