Tensile deformation of nanocrystalline ZrO2 + 5 mol% Y2O3 at temperatures in the range of 1283-1403 K is described. It is demonstrated (a) that steady state flow is possible at temperatures of the order of 0.42 T-m, where T-m is the absolute melting point, (b) that 70% engineering strain could be obtained at 1403 K (0.46 T-m), and (c) that significant grain boundary sliding was present during deformation. Static and dynamic grain growth as also a decrease in the relative density of the specimen with deformation could be observed. The present results as well as those of Owen and Chokshi concerning superplastic flow in sub-microcrystalline materials taken from literature could be accounted for quantitatively using the grain boundary sliding controlled flow model of Padmanabhan and Schlipf, originally proposed for microcrystalline superplastic alloys.