The commercially available TiO2-catalyst (Degussa P25) was supported by spray pyrolysis deposition method on the outer surface of the quartz tubes, incorporated in photocatalytic reactor. The crystal structure and the morphology of the films were studied. The immobilized TiO2 is modified with nanosized gold particles by the photoreduction method to obtain different noble metal loading (0.05-0.4 wt.%). The characterization of the synthesized catalysts was carried out by the BET method, X-ray photoelectron spectroscopy (XPS), SEM, TEM and the adsorption of the model pollutant was determined. The degradation of oxalic acid has been studied in aqueous solution photocatalyzed by band-gap-irradiated TiO2, modified with nanosized gold particles. The presence of low amounts of gold on the TiO2 surface leads to an increase of its photocatalytic activity. The maximum value of the photocatalytic activity was registered with the approximate to 0.16 wt.% Au on TiO2 sample. At this concentration the activity of the Au-modified TiO2 is approximately double that of the semiconducting support. The adsorption properties of the catalysts, as well as the noble metal content on the surface of the support, influence the efficiency of the photocatalytic process. The reaction rate of photocatalytic degradation of the oxalic acid follows a zero kinetic order according to the Langmuir-Hinshelwood model. (c) 2006 Elsevier B.V. All rights reserved.