The effect of MoO3 addition to alumina supported vanadia catalysts on the catalytic activity for the selective catalytic reduction of NO is investigated. Upon the addition of MoO3, catalytic activity is enhanced and the particle size of V2O5 which is shown by the results of XRD and Raman spectroscopy is decreased. The MoO3-V2O5/Al2O3 catalyst also exhibits more resistance to SO2 deactivation than V2O5/Al2O3 does.