Various experiments were conducted to improve durability against SO2 by impregnating the same amount of vanadium in TiO2. which had the various physical properties. According to those catalysts, the degree of deactivation by SO2 had various results, and it was found that the production of unreacted NH3 in selective catalytic reduction reaction should be low. Based on X-ray photoelectron spectroscopy analysis, O-2 on-off test, O-2 reoxidation rest and H-2-temperature programmed reduction experiment, the redox capacity of catalyst was improved due to increasing of non-stoichiometric compounds. Such a non-stoichiometric oxide and redox capacity of catalyst can be enhanced by the ball-milling process, and the production of ammonium sulfate salt can be more easily inhibited by the Superior oxidation-reduction capacity of catalyst. We found that this result is caused by producing and increasing of Vx+ (x <= 4), Tiy+ (y <= 3) which are non-stoichiometric chemical species of catalyst. Published by Elsevier B.V.