The influence of SO2 on the performance of Ag-Pd/Al2O3 for the selective catalytic reduction (SCR) of NOx with C2H5OH was investigated experimentally. The activity test results suggest that Ag-Pd/Al203 shows a small activity loss in the presence of SO2 when using C2H5OH as a reductant. In situ DRIFTS spectra show that the activity loss originates from the formation of surface sulphate species on the Ag-Pd/Al2O3. The surface sulphate species formation inhibits the formation of nitrate, whereas hardly changes the partial oxidation of C2HsOH. Compared with the NOx reduction by C3H6 an obvious suppression of the surface sulphate species formation was observed by DRIFTS experiment when using C2H50H as a reductant. This phenomenon reveals the better catalytic performance and strong SO2 tolerance of Ag-Pd/Al2O3-C2H5OH system.