The promotion of Ag/gamma -Al2O3 by adding alkali metals (Li, Na, K, Cs) for selective catalytic reduction of NO with C3H6 was studied in this work. The activity of NO reduction was enhanced by addition of Cs to Ag/gamma -Al2O3 in the presence of excess oxygen and SO2. The stability and growth of silver oxide particles were promoted and the dispersion of silver particles on gamma -Al2O3 was improved by the addition of 0.5 wt% Cs and 1 wt% Cs to 2 wt% Ag/gamma -Al2O3, respectively. The results were confirmed by H-2 TPR, UV-Vis DRS, TEM, and XPS.