Effect of pre-treatment on the gas nitriding process of austenitic stainless steels has been investigated and the following results were obtained. Minimum pre-treatment time was decreased to 5min with increasing treatment temperature from $200^{circ}C$ to $600^{circ}C$. Surface activation effect by the pre-treatment was maintained in the air up to holding time of 64hr, judging from the analysis result of gas nitrided specimens. The Depth of nitrided layer of STS 304 and 316 stainless steels were ranged from $5{mu}m$ to $90{mu}m$ at $440^{circ}C{sim}600^{circ}C$. The X-ray diffraction intensity for austenitic stainless steels were increases as nitriding temperature from $440^{circ}C$ to $600^{circ}C$.