We report the surface modification of PS films treated in aqueous ammonia solution and distilled water by a combination of ozone aeration and UV irradiation. The surface properties of the treated film were investigated by contact angle measurements, X-ray photoelectron spectroscopy (XPS), and attenuated total-reflection FT-IR (ATR/IR) measurements. The water contact angle of the treated films decreased with increasing treatment time and the film surface became hydrophilic. Treatment in aqueous ammonia solution introduced amide or amino-groups onto the PS surface. Hydroxyl groups and carbonic acid were also produced on the surface by treatment in aqueous ammonia solution. However, the treatment in water introduced only hydroxyl and carbonyl groups onto the surface. The introduction of amine and amide onto the PS film surface is due to the reaction of the PS film with amino radicals, the reaction of ammonia with reactive species on the PS film, and the ammonolysis of esters formed on the PS surface. (c) 2004 Elsevier B.V. All rights reserved.