Adsorption of the monovalent cations Cs+ and Na+ from mixed solutions of NaCl and CsCl at the TiO2 (anatase)/water interface was studied. Higher adsorption of Cs+ than Na+ was observed from solutions of similar electrolyte concentration. The surface ionization and complexation constants of surface hydroxyl groups were determined using potentiometric titration data, Results for the adsorption of Cs+ and Na+ from mixed electrolyte solutions showed that these ions adsorb at different distances from the metal oxide surface.