The reactivity of ternary V2O5-WO3/TiO2 de-NOx catalysts (V2O5 = 0-1.47% w/w, WO3 = 0-9% w/w) in the selective catalytic reduction (SCR) reaction is investigated under steady-state and transient conditions. The results indicate that over the investigated catalysts the SCR reaction occurs via a redox mechanism and that the rate-determining step of the reaction is the catalyst reoxidation process. The reactivity of the V2O5-WO3/TiO2 catalysts increases on increasing either the V2O5 or the WO3 loading; the reactivity of V and/or W in the ternary catalysts is higher than that of the corresponding binary samples. A synergism between the TiO2-supported V and W surface oxide species in the SCR reaction is suggested, that is exploited in the enhancement of the catalyst redox properties of the samples. Accordingly, tungsta increases the rate of the SCR reaction of V2O5/TiO2 catalysts by favoring the catalyst reoxidation by gas-phase oxygen.