In this study, sulfnitriding treatments were performed to improve the properties of wear resistance of AISI4140 as steel for machine structural use. Prior to these plasma treatments, a thick compound layer, a thickness of 7 to 10 μm, was formed on the surfaces of the specimens, after which the sulfnitriding treatments were performed in the same chamber. Plasma nitriding was carried out at 813 K for 2 h in an atmosphere of 75 vol% N2 and 25 vol% H2 in addition to C2H2 flowing at 50 sccm. To form a sulphide layer of about 2 to 5 μm in thickness, we carried out plasma sulfnitriding at temperature of 723 K-813 K for 2 h in the plasma nitriding in addition to H2S flowing at 100 sccm. The friction coefficient of AISI 4140 steels was reduced to 0.4 by changing the process temperature during plasma sulfnitriding. The wear volume loss also were decreased with increasing sulfnitriding process temperatures.