There are disclosed zirconia ceramics consisting mainly of Zr0 2 and Y 2 0 3 in a molar ratio of Y 2 O 3 /ZrO 2 of 2/98-7/93 and consisting of crystal grains having a mixed phase comprising a tetragonal phase and a cubic phase or having a phase comprising a tetragonal phase, the average size of the crystal grains being not larger than 2µm; such ceramics have a high strength and undergo little deterioration in strength with lapse of time.
There is also disclosed a method of producing such zirconia ceramics, by mixing zirconium oxide having a crystallite size of not larger than 1,000 A or amorphous zirconium oxide with an yttrium compound in the above mixing ratio, moulding the mixture into an article, and firing the moulded article at 1,000 to 1,550 °C.