Austenitic stainless steel in conventional and ultrafine-grained states is studied by impact testing in an unirradiated condition and after neutron irradiation to 12 dpa at 350 degrees C. We show that grain refinement provided higher resistance of the steel to the onset of evolving macrodefects (such as cracks) in irradiated state. Impact toughness of the coarse-grained steel notably degraded after irradiation, while the ultrafine-grained steel demonstrated better resistance of impact toughness to irradiation effect. This finding highlights the promising potential of ultrafine-grained steels to be used as advanced radiation resistant materials with enhanced mechanical performance. (C) 2020 Elsevier B.V. All rights reserved.