A series of characterizations including TEM-EDS, XRD, FTIR, SO2 + O-2 TPD, XPS, H-2-TPR and NH3-TPD has been carried out to explore the mechanism of the promoting effect of Cu addition on the SO2-resistance of the Ce-Ti oxide catalyst. SO2 had been found to strongly interact with surface cerium oxygen and result in the reduction of Ce4+ to Ce3+ on the Ce-Ti oxide catalyst. The Cu atoms in the Ce-Cu-Ti oxide catalyst will preferentially interact with SO2 and preserve the adjacent Ce4+. The redox ability of the Ce-Ti catalyst was found to significantly decrease due to the sulfation by SO2. Due to the formation of CuSO4 and the preserved Ce4+, the reducibility of the Ce-Cu-Ti catalyst has not significantly decreased like the Ce-Ti catalyst but slightly decreased to an adequate level for SCR reaction after sulfation. The surface acidities of Ce-Ti and Ce-Cu-Ti were both enhanced by sulfation. The preservation of the redox ability and the increase of surface acidity after sulfation had caused Ce-Cu-Ti to be a high SO2-resistance catalyst for SCR reaction. A graphical description of the effect of the Cu addition on the SO2-resistance of a Ce-Ti oxide catalyst has also been proposed. (C) 2011 Elsevier Ltd. All rights reserved.