Electrochemical surface nitriding of SUS 304 austenitic stainless steel was investigated in a molten LiCl-KCl-Li3N system at 773 K, and surface hardening by this molten salt electrochemical process without any special pretreatment was confirmed. From X-ray photoelectron spectroscopy and X-ray diffraction analyses, it was found that the surface nitrided layer contained CrN precipitates in Fe-Ni matrix. The square of the thickness of the surface nitrided layer was proportional to the electrolysis time. The rate constant, K-P, increased as the applied potential was more positive. This finding indicated that the chemical potential of adsorbed nitrogen (N-ads) on SUS 304 stainless steel electrodes depended on the applied potential and it affected nitrided layer growth. Furthermore, surface nitriding of a SUS 304 stainless steel tube was achieved. It was confirmed that adhesive coherent nitrided layers formed both on the outside and inside of the tube. These results suggested that this electrochemical surface nitriding process can be applied to specimens of various shapes. (C) 2004 The Electrochemical Society.