It has been revealed that magnesium acetylacetonate ([Mg-II(acac)(2)]) irreversibly adsorbs on TiO2 from an EtOH and n-hexane mixed solution via a one-to-one stoichiometric ligand exchange of acac(-) for Ti-s-O-, whereas it hardly adsorbs on MgO. The successive oxidation of the resultant surface complex (Mg-II(acac)-(OTis)) formed a MgOx submonolayer on the surface of TiO2. Six-time repetition of the adsorption-oxidation process achieved an approximate MgOx monolayer owing to the selective adsorption of [Mg-II(acac)(2)] on the portion of naked TiO2. The rate of the TiO2 photoinduced oxidation of sodium dodecylbenzenesulfonate increased with the MgOx submonolayer coverage (theta congruent to 0.5) by a factor of 1.3.