Austenitic stainless steel has been irradiated with metallic-ions and gas ions in order to perform a surface modification of stainless steel. An irradiation effect in stainless steel has been investigated by means of GXRD and CEMS, which show good surface-sensitivity. Metallic-ion irradiation in 17/7 stainless steel has induced the martensitic α phase, especially in the irradiation of Fe ions. Furthermore, a few kinds of gas ions has been used to induce the α phase in 304 stainless steel. It has been shown by GXRD and CEMS that Xe ion irradiation is most effective to induce the α phase in 304 stainless steel. In the case of rare-gas ion irradiation, the degree of the phase transformation has increased with increasing mass of ion species. On the other hand, the formation of the a phase has not occured in stainless steel after N₂ ion irradiation. Therefore, we conclude that Fe ion and Xe ion irradiation are suitable to perform a surface modification in stainless steel.