Abstract: Nanocrystallinemetals are defined as metals with an average grain size in the$(1\sim100)\,$nm range. Because of their potential applications inmechanics, thermodynamics,acoustics, electronics, and magnetics, etc, their manufacture and researchhave been an important frontier, both in materials science and the relatedfields. Their relative simple microstructures and characterizing parametersimpose a fundamental meaning in theoretical studies. The three-dimensionaltopology of nanocrystalline metals is similar to their conventionalcounterparts. However, for the extremely small grain size, the volumefraction of grain boundaries increases greatly, which will lead to differentmechanical properties from coarse-grained metals. Moreover, when thecharacterized lengths of the microscopic physical processes compare to thegrain size, the related properties will be modulated and thus different fromwell-known ones. In this paper, we present some new developments ofpreparation, mechanical properties and plastic deformation mechanisms innanocrystalline metals and discuss the relationships between microscopicstructures and mechanical properties.