A series of V2O5-WO3/TiO2 catalysts physically mixed with several Fe2O3 samples having different textural properties were prepared and applied to the selective catalytic reduction (SCR) of NOx with NH3. The physically mixed catalysts exhibited higher catalytic stability and SO2 resistance than the V2O5-WO3/TiO2 catalyst in the presence of SO2. The physicochemical properties of V2O5-WO3/TiO2 catalysts physically mixed with Fe2O3 were investigated by various analytical techniques, such as N2 adsorption-desorption, X-ray diffraction (XRD), Raman spectroscopy, temperature-programmed desorption with sulfur dioxide (SO2-TPD) and ammonia (NH3-TPD), and in situ Fourier-transform infrared spectroscopy (FT-IR) measurements. The formation of ammonium sulfate species was observed in the catalysts during the NH3-SCR reactions, leading to deactivation of the catalysts. SO2TPD analyses revealed that Fe2O3 adjacent to V2O5-WO3/TiO2 suppressed the formation of ammonium sulfate species by generating iron sulfate species. In addition, the in situ FT-IR and NH3-TPD results indicated that the adsorption of SO2 on Fe2O3 could increase NOx conversion due to the additional production of Bronsted acid sites provided by iron sulfate. Among the catalysts tested, the mechanical mixture of V2O5-WO3/TiO2 and Fe2O3, with the highest surface area and pore volume, showed the best NH3-SCR activity and SO2 resistance at low temperature in the presence of SO2.