Effects of tungsten on vanadium-based catalysts were studied under differently dispersed conditions of tungsten oxide on titania surface. Acidity, surface species and NH₃-SCR performance over commercial WO₃/TiO₂ and V₂O₅WO₃/TiO₂ have been investigated. The incomplete dispersion of tungsten oxide gives rise to the formation of crystalline WO₃ on titania surface, and the mounts of surface Brønsted acid sites decrease consequently. From the TPR and Raman spectra, it is indicated that two-dimensional vanadium species exhibits a tendency to moderately anchor onto titania surface in the immediate vicinity of tungsten species. It is also found that amorphous tungsten oxide has different impacts on the dispersion of vanadium species over titania surface at variable loadings of vanadia. At low vanadium loadings, amorphously distorted tungsten species show promoting effects on the formation and dispersion of two-dimensional vanadium species. With vanadium loadings increasing, amorphous tungsten species exert compressing effects on surface vanadium species and lead to the aggregation of vanadium oxide.