It is well established that cavitation occurs in most materials during superplastic deformation, and cavitation has an effect on elongation to failure and mechanical properties of the materials after deformation. The cavities most likely nucleate at grain boundary particles or at triple points in quasi-single phase materials, at triple points and grain boundary ledges in microduplex materials and at particulate or whisker reinforcement in metal matrix composites. To minimize cavitation during superplastic flow it is necessary to exercise sound microstructural control. The starting materials should be processed to develop a fine uniform grain size and if dispersions are present, these should be fine and uniformly dispersed. In the present study, the effect of grain size on superplastic deformation and cavity formation in 3 mol% yttria-stabilized zirconia polycrystal has been examined. Also the distribution of cavity size and circularity have been quantitatively determined as a function of grain size. The results demonstrated that extensive internal cavities formed during high temperature deformation and the amount of cavitation increased with increasing grain size. (C) 2002 Elsevier Science Ltd and Techna S.r.l. All rights reserved.