In this study, Ag supported on TiO2, SiO2, and SiO2-TiO2 catalysts were prepared through the impregnation method and their performance for the selective catalytic oxidation of ammonia (NH3 -SCO) was tested. The results showed that the Ag/SiO2-TiO2 (denoted as Ag/Si-Ti) performed at a much higher activity than Ag/TiO2 and Ag/SiO2 at low temperature range. Characterization results revealed that SiO2 possessed a high surface area, but lacked OH groups and acidic sites; TiO2 possessed abundant OH groups and acidic sites, but the surface area was low. High surface area and abundant OH groups were a benefit for the dispersion of Ag, and acidic sites contributed to the adsorption and activation of ammonia. The synergistic effect compromised the advantages and disadvantages of SiO2 and TiO2, which improved the dispersion of Ag, enriched acidic sites of the catalyst and maintained Ag-0 content at an appropriate level, therefore enhanced the NH3-SCO activity of Ag/Si-Ti catalyst.