The synthesis of nanocrystalline materials has provided new opportunities to explore grain size dependent phenomenon to a much finer scale. Superplasticity is a well-established grain size dependent phenomenon. In this paper, we analyze some of the tensile superplasticity data obtained in the last few years on Ti-6Al-4V, Ni(3)Al, and 1420-Al alloy processed by severe plastic deformation (SePD). The experimental results show higher flow stresses for superplasticity in nanocrystalline materials than in microcrystalline materials. It is suggested that the conventional slip accommodated grain boundary sliding is likely to be difficult in nanomaterials.