Work was carried out to clarify heterogeneities in the structure of a commercial PSZ containing 2. 5 mol%Y//2O//3 and observe microstructural changes with post annealing. Besides coagulated Al//2O//3 inclusions, Y//2O//3 concentration fluctuated in the range from 2 to 3 mol%. When the compact was annealed at 1673 K, grains in the Y//2O//3 enriched zone (cubic ZrO//2) grew preferentially. The difference in Y//2O//3 concentration decreased with annealing temperature and became almost equal at 2243 K.