In our study nanocomposites of TiO2-Au and ZnO-Au core-shell nanoparticles have been prepared via colloidal chemical method. The particle size, shape and chemical composition have been determined via high resolution transmission electron microscope (TEM) and X-ray diffraction (XRD) analysis. These nanomaterials have been used as a photocalalysts for photodegradation of organic waste for water purification. Primicarb is one of the most commonly used pesticides in Egypt, the degradation of 20 ppm primicarb under ultraviolet (UV) and visible light in the presence and absence of TiO2, TiO2-Au, and ZnO-Au nanocomposite was analyzed with high performance liquid chromatography (HPLC) and UV-Visible Spectra. The rate of the photodegradation and the catalytic activity of these nanomaterials have been determined and compared. The results indicate that the core-shell nanoparticles is much more active catalyst in presence of sun light than pure TiO2 nanomaterials which has absorption maximum at 370nm.