Mesoporous iron oxide-silica composite with a high silica content was synthesized by hydrothermal method,and another composite material with a high iron content was obtained by etching part of silica in alkaline solution.Gold catalysts were loaded onto both composites by a deposition-precipitation method,and used for CO oxidation.The samples were characterized by BrumauerEmmet-Teller(BET),X-ray diffraction(XRD),X-ray photoelectron spectra(XPS),transmission electron microscope(TEM)and scanning electron microscope(SEM)techniques.Both composites had high specific surface areas and were amorphous.The Au nanoparticles dispersed on the surface of the composites existed in metallic state.Composite with high silica content was not suitable for Au loading,and its supported gold catalyst showed poor performance in catalytic reaction.In contrast,composite with high iron content allowed efficient Au loading,and CO could be oxidized completely at low temperature on its supported gold catalyst.The effects of deposition-precipitation pH values on Au loading and activity of the catalyst were investigated,and the results indicated that Au loading was the highest and the catalyst was the most active for CO oxidation when the synthesis pH was adjusted to 8. Mesoporous iron oxide-silica composite with a high silica content was synthesized by hydrothermal method, and another composite material with a high iron content was obtained by etching part of silica in alkaline solution. Gold catalysts were loaded onto both composites by a deposition-precipitation method , and used for CO oxidation. The samples were characterized by Brumauer EMT-Teller (BET), X-ray diffraction (XRD), X-ray photoelectron spectra .Both composites had high specific surface areas and were amorphous. The Au nanoparticles dispersed on the surface of the composites existed in metallic state. Compite with high silica content was not suitable for Au loading, and its supported gold catalyst showed poor performance in catalytic reaction .In contrast, composite with high iron content allowed efficient Au loading, and CO could be oxidized completely at low temperature on its supported gold catalyst.The e ffects of deposition-precipitation pH values ​​on Au loading and activity of the catalyst were investigated, and the results indicated that Au loading was the highest and the catalyst was the most active for CO oxidation when the synthesis pH was adjusted to 8.