Abstract: A series of catalysts with manganese oxide and cerium oxide supported on monoclinic zirconia (m-ZrO₂), tetragonal zirconia (t-ZrO₂) and cubic zirconia (c-ZrO₂) were prepared by the wet impregnation method. SCR activity measurements were carried out in a fixed-bed reactor. The results revealed that all prepared catalysts showed good catalytic activity. The catalyst with 15.0% MnO_x supported on c-ZrO₂ got 100% NO conversion at 103 ℃. The activity of all prepared catalysts decreased in the following sequence:MnO_x-CeO₂/c-ZrO₂>MnO_x-CeO₂/t-ZrO₂>MnO_x-CeO₂/m-ZrO₂. To explain this phenomenon, catalysts with 5.0% MnO_x support on m-, t- and c-ZrO₂ were chosen to be further characterized. BET results suggested the surface area of the catalyst supported by c-ZrO₂ was 39.67 m²/g, which was the biggest and best one for contact between gas and active sites. XPS analytical outcomes indicated the concentration of lattice oxygen on the surface of the catalyst supported by c-ZrO₂ was the highest, which was helpful for the formation of Lewis acid sites. The total area and intensity of TPR and TPD peaks indicated that there were only Lewis acid sites on the surface of catalysts supported by c-ZrO₂ and t-ZrO₂, while both Lewis and Brnsted acid sites appeared on the surface of catalysts supported by m-ZrO₂ (though the latter was predominant). Crystal effect was attributed to the difference of surface area and acidity for different structures of ZrO₂. Cubic zirconia is the best choice for SCR catalyst support.