Two sets of WO3/SiO2 catalysts were prepared from (NH4)(6)H2W12O40(aqueous method) and W(eta(3)-C3H5)(4)(non-aqueous method). The molecular structures and dispersions of the surface tungsten oxide species for the WO3/SiO2 catalysts under ambient and in situ dehydrated conditions were investigated by Raman spectroscopy. The samples prepared from (NH4)(6)H2W12O40 (aqueous method) exhibit very strong Ramanfeatures due to the presence of crystalline WO3 and the samples prepared from W(eta(3)-C3H5)(4)(non-aqueous method) do not possess crystalline WO3. These results suggest that the preparation method exerts an influence on the dispersion of the surface tungsten oxide species on SiO2. The surface tungsten oxide species under ambient conditions possess polytungstate clusters, W12O4212-, on the silica support. Upon dehydration at elevated temperatures, the hydrated polytungstate clusters decompose and interact with the silica support via the formation of isolated, octahedrally coordinated tungsten oxide species.