In order to improve the low ductility of nanostructured materials, a layered and nanostructured (LN) 304 SS (stainless steel) is prepared from warm co-rolled 304 SS pre-treated by surface mechanical attrition treatment. The microstructure and mechanical properties, as well as strain hardening, are analyzed in details. The LN steels ex- hibit both high strength and large ductility resulting from good strain hardening behaviors. The strain hardening can be subdivided into two stages, which involves a multiple cracking along interlaminar at the first stage and a strain-in- duced martensite (SIM) transformation at the second stage. The SIM transformation of nanocrystallines and ultrafine grains induces a larger work hardening exponent by the formation of nanoscaled martensite phase. The effect of grain size on the transformation dynamics is discussed.