Abstract Since 1980 much attention has been payed to hydrothermal processing. There are several papers related to hydrothermal fine Zirconia powders by authors 1), 2), 3) and 3). The authors 3) prepared ZrO 2 and Y 2O 3-ZrO 2 powders under hydrothermal conditions. Several methods were used to prepare fine ZrO 2 powders under hydrothermal conditions: hydrothermal precipatation, hydrothermal crystallization, hydrothermal oxidation, hydrothermal decomposition, hydrothermal synthesis, hydrothermal anodic oxidation, RESA (reactive electrode submerged arc) process, etc. This paper describes hydrothermal precipatation processing of ZrO 2 and Y-ZrO 2 powder.