Transparent anatase TiO 2 nanometer thin films were prepared via the sol-gel method on soda-lime glass, and then the as-prepared TiO 2 films were treated in HCl solution. The TiO 2 films before and after treatment were characterized by X-ray photoelectron spectroscopy, scanning electron microscopy, and UV-visible spectrophotometer. The photocatalytic activity and hydrophilic property of the various TiO 2 films were evaluated by the photocatalytic decolorization of aqueous methyl orange and examining the contact angle for water of TiO 2 films, respectively. The concentration of sodium and calcium in nascent TiO 2 films was effectively reduced and the adsorbed hydroxyl content on the surface of TiO 2 films was found to increase by soaking the as-prepared TiO 2 films in HCl solution. The deleterious effect of sodium and calcium ions from the soda-lime glass on the photocatalytic activity of the nascent TiO 2 films was prevented by surface acid treatment. At the same time, hydrophilic property of the treated TiO 2 films was enhanced.