PURPOSE: To obtain excellent zirconia porcelain suitable for an oxygen sensor, by coating the surface layer of partially stabilized zirconia porcelain with a powder forming perfectly stable zirconia by baking and baking the coated porcelain to cover the surface layer with perfectly stabilized zirconia.

CONSTITUTION: A mixture consisting of 94mol% ZrO2, 5mol% Y2O3 and 1mol% Al2O3 is molded into a bag tubular shape after calcination and crushing while ethyl acetate and terpentine oil are added to a powder, which is formed by calcining and crushing a mixture consisting of 91mol% ZrO2, 8mol% Y2O3 and 1mol% Al2O3 and can form perfectly stabilized zirconia by baking, to prepare a paste. After both surfaces of the aforementioned molded body is coated with said paste, the coated one is baked at about 1,630°C for 3hr to obtain porcelain wherein a cubic system single phase perfectly stabilized zirconia layer is formed to the surface of a partially stabilized zirconia base porcelain consisting of two phases or three phases of a cubic system, a monoclinic system and a tetragonal system. By this method, electrodes are provided to both surfaces of porcelain to make it possible to form an oxygen sensor excellent in strength and thermal stability without irregularity of characteristics.