Nobuhiro Tsuji has been studying physical metallurgy and mechanical metallurgy of structural metallic materials involving both steels and nonferrous alloys. His research works cover metal working processes, heat treatments, recrystallization, phase transformation, metallography, microstructures, textures, crystallography, electron microscopy, dislocation theory, and mechanical properties of metallic materials. Especially, he has developed accumulative roll bonding (ARB) process, which is a kind of severe plastic deformation (SPD) process using rolling deformation for fabricating ultra fine grained or nano structured bulky materials, and has energetically studied the ultrafine grained and nanostructured metals fabricated by ARB and other processes. Tsuji has published many papers about the correlation between microstructures and mechanical properties of nano structured materials, which have been highly cited. He got many scientific awards including the 5th JSPS Prize.