The invention provides a process for producing an aqueous dispersion of zirconium oxide comprising: reacting a zirconium salt with an alkali in water to obtain a slurry of particles of zirconium oxide; filtering, washing, and repulping the slurry; adding an organic acid to the resulting slurry in an amount of one mole part or more per mole part of the zirconium in the slurry; hydrothermally treating the resulting mixture at a temperature of 170° C. or higher; and washing the resulting aqueous dispersion of particles of zirconium oxide.