The reduction of grain size down to several tens or hundreds of nanometers leads to the enhancement of radiation resistance of metals. Based on this approach, the aim of the Labex EMC3 (Energy Materials and Clean Combustion Center) project "Naninox" is (1) to study the stability of the microstructure of a nanostructured 316 stainless steel under ion irradiation and (2) to link between this microstructure and the properties (corrosion resistance and the microhardness) of the steel (thanks to a better irradiation resistance, a better corrosion resistance and higher mechanical properties after irradiation are expected in the ultra-fine grained stainless steel). Ultrafine grained 316L austenitic stainless steel samples have been produced by high pressure torsion (HPT) at 430°C and then ion irradiated in Jannus facilities (CEA Saclay) at 450°C and 5 displacements per atoms (dpa). Their microstructure is characterized before and after irradiation by atom probe tomography, X-ray diffraction and transmission electron microscopy. Corrosion behavior in NaCl solution is tested and nano-indentation tests are performed. The first results obtained by atom probe tomography described in this paper indicate that the microstructure of ultrafine grain 316 austenitic stainless steel is more stable under irradiation than the microstructure of a coarse grain 316 austenitic stainless steel.