PURPOSE: To produce the titled zirconium oxide powder having uniform composition, by attaching amorphous yttrium hydroxide gel to the surface of hydrated zirconium oxide powder, and calcining the oxide powder.

CONSTITUTION: An aqueous solution of a water-soluble yttrium salt (e.g. yttrium chloride) is made to react with an aqueous solution of an alkali (e.g. NaOH) at ≥8.5pH and ≤40°C to obtain amorphous yttrium hydroxide gel powder (A). Separately, an alkali is added to an aqueous solution of zirconium oxychloride, zirconium nitrate, etc., the produced gel is aged, classified by its particle size, and fractionated and recovered to obtain hydrated zirconium oxide (B). The component B is added to an aqueous dispersion of the component A, stirred, left at rest to deposit the component A to the surface of the component B, and the product is calcined at 600W1,100°C for 0.25W2hr.