The additive effect of noble metals (Rh, Ir, Ru, and Pd) on the catalytic activity of Ag/Al2O3 for the selective reduction of NO with n-decane in the presence of O2, H2O and SO2 was investigated. Although NO reduction activity of Ag/Al2O3 was decreased by coexisting SO2 at temperatures below 450°C, the addition of Rh improved the activity at 300-400°C. Optimum Rh loading was 0.05-0.1wt% and the effect was remarkably observed at low concentration of coexisting SO2.