The surfaces of fumed silica materials were modified with a surface sol-gel process for catalysis applications. This surface-modification approach allows not only a monolayer growth of TiO2 or Al2O3 but also a stepwise double-layer growth of TiO2/TiO2, Al2O3/Al2O3, TiO2/Al2O3, or Al2O3/TiO2 on the surfaces of the silica materials with a monolayer precision. XRD analyses revealed that the coated monolayers and double layers of TiO2 and Al2O3 were amorphous. Gold nanoparticles were successfully deposited on the above six surface-modified silica materials via a deposition-precipitation method. The catalytic activities of these six gold catalysts for CO oxidation are highly dependent on the structures of their surface monolayers or double layers. The gold catalyst supported on the silica material functionalized with a TiO2 monolayer (Au/TiO2) is the most active in both as-synthesized and oxidized forms, while the gold catalyst supported on the silica material functionalized with an Al2O3/TiO2 double layer (Au/Al2O3/TiO2/SiO2) is the most active in the reduced form among the six catalysts. Surprisingly, the gold catalyst supported on the silica material functionalized with a TiO2/Al2O3 double layer (Au/TiO2/Al2O3/SiO2) has much less activity than Au/Al2O3/TiO2/SiO2 under all various treatments, underscoring the sensitivity of the catalytic activity to the structure of the supporting surfaces.