An aqueous dispersion of titanium oxide particles comprising chloride ion, and a Brønsted base other than chloride ion, preferably at least one kind of ion selected from nitrate ion and phosphate ion. Preferably the titanium oxide particles are predominantly comprised of brookite titanium oxide particles. The aqueous titanium oxide dispersion is prepared by hydrolyzed titanium tetrachloride in the presence of at least one kind of a Brønsted acid. A thin film formed from this aqueous titanium oxide dispersion exhibits good photo-catalytic activity, transparency and adhesion to a base material.