Zinc oxide ZnO nanoparticles synthesized by sol-gel method and commercial titanium dioxide TiO2 were studied in the present work. The structural properties of the ZnO and TiO2 nanoparticles were determined by Fourier transform infrared (FTIR), X-ray diffraction (XRD) and Raman spectra techniques (RS). The average crystallite sizes were calculated by using the powder X-ray and were found to be 48 nm and 20 nm and the specific surface areas were about 1047 m 2 g −1 and 381 m 2 g −1 for ZnO and TiO2, respectively. The FTIR and Raman spectroscopy results have shown high purity of the ZnO and TiO2 samples and they are consistent with the one obtained from XRD. The ZnO and TiO2 nanoparticles were used as catalysts for the elimination of an azo dye, Mordant Violet 5 (MV5), in aqueous solution, by an advanced oxidation process which is heterogeneous photocatalysis. Synthesized ZnO was more efficient than commercial TiO2 to degrade MV5 under UV irradiation. The adsorption of MV5 on TiO2 and ZnO was found favorable by the Langmuir approach. The MV5 adsorption constant on TiO2 was higher than that obtained in the case of ZnO. The photocatalytic reaction of MV5 in presence of each catalyst was investigated at different concentration of the dye and at different conditions of pH. The solar radiation of MV5 in the presence of each catalyst was also tested.