Thermal stability of the nitrides formed by ion implantation of nitrogen on 304 stainless steel (304 SS), is studied using X-ray photoelectron spectroscopy (XPS). Nitrogen implantation has been carried out at room temperature (RT) at a dose of 1 ×10 18ions/cm 2on 304 SS foils. XPS spectra have been recorded at RT, 150°C, 250°C, 350°C and 500°C. It is observed that various nitride phases are formed. The major redistribution of N atoms takes place above 250°C. At higher temperatures, possibly, Fe 2 + xN phases decompose and CrN concentration increases. The evolution of nitrogen gas is also observed. The method for determining the charge transfer from the XPS shift in the case of nitrides is developed and is applied in the present work. Microhardness changes in the implanted samples were also registered and their possible correlation with the nitride formation is discussed.