PURPOSE: To prepare the titled powder having narrow particle size distribution and being useful for fine ceramic by heating and hydrolyzing aqueous suspension obtd. by adding a Zr salt to monoclinic zirconia agglomerated particles in acidic condition causing crystal growth.

CONSTITUTION: Aq. soln. of a Zr salt (e.g. ZrOCl2.8H2O) is hydrolyzed by heating to obtain agglomerated paticles of monoclinic zirconia having ≥ca.1,000 particle size. An aq. suspension comprising the agglomerated particles and Zr salt is admixed with an acid to adjust the pH to ≤1, and the suspension is hydrolyzed by heating at 90W250°C while keeping the suspended particles in suspended state. Crystals are grown to ≥3,000 from the obtd. suspended particle as seed crystal. The grown crystals comprise secondary particles consisting of monoclinic superfine primary particles having ≤100 crystallite size being agglomerated orientedly. Thus, a powder body consisting of almost spherical agglomerated zirconia particles having 0.3W3μm particle size is obtd.