Stainless steel type 304L has been nitrided in the low pressure (600Pa) and high nitrogen (80% N₂+20% H₂) environment for 5 hours by the square-wave-pulsed-d.c. plasma as a function of temperature 400∼550℃ and pulsation. At the lower temperature range of 400∼500℃ and at the relatively high ratio of pulse duration to pulse period. "S-phase" has been developed in the form of thin nitrided surface layer which has many cracks, leading to be nearly impossible for the industrial anti-wear and anti-corrosion applications. At the higher temperature up to 550℃ with the increasing ratio of the pulse duration to pulse period up to 50㎲/100㎲, the nitrided layer, whose growth rate has increased also, has been composed mainly of CrN and Fe₄N phases and has become thick, uniform and nearly crack-free.