The performance of mixed niobium-zirconium oxide in the SCR of NOx with propene in excess oxygen has been studied. The mixed oxide is prepared by impregnation of hydrated zirconia with acidic solution (pH 0.5) of peroxoniobium(V) complex, [Nb-2(O-2)(3)](4+), ensuring ZrO2:Nb2O5 mole ratio of 6:1. The calcined sample (denoted as 25NbZ-P) has the structure of Zr6Nb2O17. According to the catalytic test, the conversion of NOx over the 25NbZ-P catalyst passes through a maximum at 220 degrees C. Based on the in situ FT-IR results, a reaction mechanism is proposed with nitroacetone and NCO species as the key reaction intermediates. The results of the investigation show that the catalytic properties of the Zr6Nb2O17 solid solution could be of interest regarding the development of low-temperature catalyst for the SCR of NOx with hydrocarbons.