Agglomerated nanocrystalline ZrO2-8%Y2O3 powder prepared by spray drying was heat-treated in air at temperatures from 1 200 ℃ to 1 400 ℃ for 2 h. Scanning electron microscopy was used to examine the changes of particle size and morphology,and X-ray diffraction was used to analyze the change of constituent phases before and after the high temperature heat treatment.Nano-particle growth behavior was also investigated. The results show that the major constituent phase of the agglomerated nanocrystalline powder is tetragonal, and non-uniform growth of the nano-particles occurs while the heat treatment temperature reaches 1 300 ℃. This non-uniform growth phenomenon is related with the inhomogeneous distribution of Y2O3 in ZrO2.Nano-particles grow into micron particles through the mechanisms of gradual merging of nano-particles in some areas and sudden merging of nano-particles in other areas.