In this work, the microstructure and wear behavior of plasma nitrided - oxidized AISI 316 austenitic stainless steel was investigated. The structural, mechanical and tribological properties were analyzed by using XRD, SEM, EDS, microhardness testing and pin-on-disk tribotesting respectively. The plasma nitriding treatment was performed at 425, 450 and 475°C for 5 h with gas mixture of N 2 /H 2 : 1/3 and 10 torr pressure. Plasma nitriding at 450 °C for 5 h produced single nitrided layers with thickness about 14 mm. Structural analysis indicate that the single phase produced was free from chromium nitride precipitation and possesses all the characteristics of the nitrogen S-phase formed in DCPN. Furthermore, supersaturation of nitrogen in the S-phase has expanded the F.C.C. lattice structure of the substrate, and thus shifted the corresponding XRD peaks of the substrate austenite to lower. The expanded austenite ? N {200} planes are more widely shifted than any other planes indicating a deviation from the cubic F.C.C. The shift of the austenite peaks to lower angles indicates compressive residual stresses in the nitrided layer. Subsequently, the treatment of plasma nitriding - oxiding was performed with optimum parameter of plasma nitriding and oxiding temperature of 400, 450 and 500°C with gas mixture of O 2 /H 2 : 1/5 for 15, 30 and 60 min. The maximum surface hardness was obtained at plasma nitrided specimen due to the hard nitrided S-phase (1350 HV 0.025 ) but the oxide layer formed caused the decrease of the surface hardness (500-550 HV 0.025 ). This can be ascribed to the lower hardness of iron oxide than iron nitrides. It can be seen that a single phase magnetite (Fe 3 O 4 ) was produced at all oxidation treatment. The nirtided layer thickness was reduced with increasing of the oxidation time in all oxidation temperatures. But oxide layer thickness was increased at 400 and 450°C and reduced at 500°C with increasing of oxidation time.