The conventional Stober method is used to prepare silica microsphere in different alcohol solutions. The influence of different alcohol solvent on the size of silica is discussed. The results indicate that the diameter of silica is gradually increased with the molecular weight of methanol, ethanol, propyl alcohol and buthanol and the mechanism is also discussed subsequently. Taking the silica prepared as a carrier, SiO2/Ag composites by adsorption and chemical reduction are obtained. The SiO2/Ag composites are very sensitive to golden brown staphylococcus and Escherichia coli with the inhibition zone diameter of 15.3 mm and 10.4 mm respectively.