A series of nano-size gold catalysts were prepared by deposition-precipitation method using silica material promoted with different amounts of MgO as the carrier.The influences of MgO addition on the structure and property of the nano-size gold catalysts were characterized by X-ray diffraction (XRD),transmission electron microscopy (TEM),O2 temperature-programmed desorption (O22-TPD),and inductively coupled with plasma atomic emission spectroscopy (ICP-AES) techniques.The total oxidation of CO was chosen as the probe reaction.The results suggest that for the gold catalysts supported on the silica material after MgO modification,the size of the gold particles is pronouncedly reduced,the oxygen mobility is enhanced,and the catalytic activity for low-temperature CO oxidation is greatly improved.The gold catalyst modified by 6 wt％ MgO (Mg/SiO2 weight ratio) shows higher CO oxidation activity,over which the temperature of CO total oxidation is lower about 150 K than that over the silica directly supported gold catalyst.