A dynamic kinetic study of the undesired oxidation of SO2 over a commercial V2O5-WO3/TiO2 monolith catalyst for the SCR-DeNO(x) process is herein presented. Transient SO2 conversion data were systematically collected during experiments involving step changes of temperature, area velocity, and feed composition (SO2, O-2, H2O, and NH3). Characteristic times of the system response were of a few hours: peculiar SO3 emission peaks were apparent upon increasing the reaction temperature and the H2O feed content. The data were well interpreted by a dynamic kinetic model assuming that buildup-depletion of surface sulfate species is rate controlling. The model accounts successfully also for the transient effects resulting from the interaction between the SCR-DeNO(x) reaction (NOx reduction with NH3) and the oxidation of SO2.