This study has been carried out to the low temperature plasma nitriding treatment on the mechanical properties of stainless steel at temperature range between 400˚C and 500°C. It was found that there was precipitated to free CrN matrix below 400˚C and there was precipitated S-phase of STS 316L, ε-phase of STS 409L and αN-phase of STS 420J2. STS 316L has formed relatively abundant CrN phase and γ`-Fe4N phase at 500˚C, alternatively STS 409L and STS 420J2 were more deeply nitrided than STS 316L at 500˚C.