A series of SnO 2 doped Ce-Ti-O x catalysts were prepared by using the hydrothermal method. The Ce 0.2 SnTiO x catalyst exhibited much higher activity than any other SnO 2 modified Ce-Ti-O x and Ce 0.2 TiO x catalysts for the selective catalytic reduction of NO x with NH 3 in the temperature range from 100 to 400°C. The Ce 0.2 SnTiO x catalyst also showed higher anti-poisoning ability to the SO 2 and H 2 O at 300°C. The BET analysis results showed that the structure parameters of the Ce-Sn-TiO x catalyst were improved by doping with SnO 2 . XRD results displayed that some interaction existed among Ce, Sn and Ti in the Ce-Sn-TiO x catalyst. The H 2 -TPR result suggested that the reducibility of the Ce 0.2 TiO x was also enhanced by modifying with SnO 2 . The NH 3 -TPD and in situ DRIFTS indicated that the introduction of SnO 2 could increase the surface acid sites and enhance the adsorption ability to the NH 3 and NO x on the catalyst surface, which are the critical factors for the improving the NH 3 -SCR performance.