Control of the surface structure of titanium dioxide thin film photocatalysts was successfully carried out by a polymer-doped dip-coating process. The thin films prepared were either transparent or opaque, depending on the molecular weight of the polymer doped. All the thin film photocatalysts had anatase form with similar crystallinity. The surface of the transparent thin films looked plain consisting of uniformly aggregated nanometer-size TiO2 particles, while the opaque thin films were formed of cubic crystalline TiO2 at the micrometer level. Both the transparent and opaque films showed catalytic activity for the elimination of NOx in air. The specific surface area and photocatalytic activity of the transparent thin film was almost the same as that of the opaque one. The activity of the thin films was almost equal to the commercial photocatalyst P25. Decrease in the film thickness led to a decrease of the elimination of NO in air by the thin films. The thin films were porous and the surface area was dependent on the film thickness. Adsorbed NO was photooxidized to NO2 by the thin films, while the NO2 formed was re-photooxidized to HNO3 before the desorption of NO2 from the film surface.