In this study, the wear behaviour of carburized and carbonitrided AISI 1020 and 5115 steels, widely used in industry, were investigated. The surface properties, microstructures, hardness distributions and wear behaviour of the treated steels were determined as well as the wear characteristics and weight losses of the treated samples as a function of wear test durations and loads. The results indicated that the surface of carbonitrided steel have epsilon-carbonitride compound layer and diffusion zone with chromium iron carbide (Cr, Fe)(7)C-3, chromium carbide nitride (Cr(6)2C(3) . 5N(0.3)), chromium nitride (Cr2N), [Cr, Fe(2N(1...x))] and Fe2N phases. The surface hardness and wear resistance of the carbonitrided samples are higher than those of the carburized samples. The carbonitrided 5115 steel has the highest wear resistance followed by carburized 5115, carbonitrided 1020 and carburized 1020 respectively. (C) 1997 Elsevier Science B.V.