A series of CeO2/Al2O3 and CeMoxOy/Al2O3 catalysts were prepared by an extrusion method for selective catalytic reduction of NOx, and were characterized by techniques of XRD, XPS, N-2-BET, H-2-TPR and NH3-TPD. Promotional effects of molybdenum additives on catalytic performances and tolerances toward SO2 and H2O poisoning of the catalysts were comparatively studied. Results showed that the CeO2/Al2O3 catalyst with the Ce/Al molar ratio of 1:5 exhibited the best catalytic performance; molybdenum additives greatly improved catalytic performance of the CeMoxOy/Al2O3 catalysts, and the catalyst with the Al/Ce/Mo molar ratio of 5:1:0.15 calcinated at 550 A degrees C exhibited the highest catalytic activity above 95 % in active temperature window of 250-430 A degrees C under the gas hourly space velocity (GHSV) of 7200 h(-1). Moreover, molybdenum additives broadened the range of the active temperature, and significantly enhanced the anti-sulfur poisoning ability. Analysis showed that the promotional effects of molybdenum additives were attributed to the improvement of specific surface area, increment of surface acidity and the enhancement of the redox properties.