Because a stainless steel has an excellent corrosion resistance, it has been used in various fields such as daily necessities, automobile components, and chemical plants. However, it is well known that a stainless steel has a poor wear resistance resulted from its low hardness. Surface modification technique for improving the wear resistance is desired without deteriorating the excellent corrosion resistance. In the present study, nitriding treatment of a sus304 stainless steel was carried out using a newly developed plasma nitriding apparatus. X-ray diffraction analysis revealed that nitrides formed on the specimen surface were a S-phase and CrN. Nitriding-time progress brought about the thickness growth of nitrides. Simultaneously, lattice strain and amount of solid solution of nitrogen atom were increased significantly. The wear characteristics of nitrided sus304 had the thickness dependence of S-phase. In particular, the thickness increase of S-phase resulted in decrease of the wear volume. CrN showed inferior wear characteristics than S-phase due to brittle mechanical properties of its.