To provide a rare earth element-doped metal oxide, a method for producing the same, particularly, a metal oxide-dispersed transparent sol aqueous solution in which nanoparticles of the rare earth element-doped metal oxide are dispersed excellently, and an advantageous method for producing the metal oxide-dispersed transparent sol aqueous solution.

The method for producing the basic metal oxide-dispersed transparent sol aqueous solution comprises: the first step of subjecting metal salt, rare earth element-containing salt and quaternary ammonium salt to a neutralization reaction to produce an aqueous solution containing an anionic, basic, and inorganic metal complex; and the second step of hydrothermally treating the aqueous solution produced at the first step.