Abstract: AISI 1020 steel was co-permeated with carbon and nitrogen. The friction and wear behavior of the co-permeated surface-modified layer in dry sliding against AISI-C-52100 steel at extremely high speed from 25m/s to 35m/s and under relatively low loads from 2N to 6N was examined on a pin-on-disc test rig. The morphologies of the worn surface and the wear mechanism of the surface-modified layer were observed and analyzed by means of scanning electron microscopy and X-ray photoelectron spectroscopy. The results show that the wear rate of the surface-modified layer decreases greatly with the increase of the sliding speed when the sliding speed is below 35m/s, then the wear rate assumes a considerable increase with increasing sliding speed. The variation of the wear rate with the sliding speed is closely related to the generation and spalling of the oxide film on the worn surface. Namely, the oxide film is composed of Fe 2O 3 at a relatively smaller sliding speed but of FeO at a larger sliding speed.