Abstract: Three kinds of carriers TiO₂, TiO₂-ZrO₂ with the molar ratio of 1:1, and TiO₂-ZrO₂ with the molar ratio of 4:1 were prepared by a sol-gel method, and then the corresponding catalysts were obtained through loading a certain amount of active ingredient MnO_x on the carriers. The carriers and catalysts were characterized by X-ray diffraction (XRD) and scanning electron microscopy (SEM). Some experiments on the selective catalytic reduction of NO with ammonia (NH₃-SCR) were performed in order to investigate the activity of the catalysts. It is found that TiO₂-ZrO₂ (4:1) has the minimum particle size and its particles are highly dispersive among the three carriers. When adding ZrO₂, Zr⁴⁺ ions dope into the TiO₂ lattice by substituting Ti⁴⁺ ions, and thus the lattice distortion is triggered and the crystal transformation is restrained in the TiO₂. Furthermore, Zr also promotes the dispersion of the active ingredient on the carrier, thereby improves the activity of the catalysts. The 10%Mn/TiO₂-ZrO₂(4:l) catalyst that adding 10% Mn to TiO₂-ZrO₂(4:l) has the highest activity among the three catalysts. The conversion of NO can reach 92.6% when catalyzed by this catalyst at 130℃. The activity of 10%Mn/TiO₂-ZrO₂(4:l) decreases when adding 10% of water vapor at 150℃, and it can restore when cutting off water vapor. But water vapor has no effect on the activity of 10%Mn/TiO₂-ZrO₂(4:l) at 200℃.