Severe plastic deformation and intense single-beam He-ion irradiation were performed on a nanostructured(NS)reduced activation steel and its coarsen-grained(CG)counterparts to make comparative study of irradiation-induced microstructure evolutions.A surface layer with a depth-dependent NS microstructure was prepared in the reduced activation ferrite/martensitic(RAFM)steel using surface mechanical attrition treatment(SMAT).Microstructure evolutions after Ar irradiation at room temperature were investigated using Transmission Electron Microscope(TEM).Experimental observations show that grain boundaries(GBs)play an important role during irradiation.Void-denuded zones were observed in both of the NS samples and CG sample,and He bubbles distributed along GBs are also observed.However,compared with the bubbles in CG sample under the same irradiation,bubbles with smaller density and larger size were observed in NS sample.This phenomenon can be attributed to the absorption of irradiation-induced point defects by GBs/interfaces in NS sample.