The effect of sulfated CaO on NO reduction by NH3 in the presence of excess oxygen was investigated to evaluate the potential of simultaneous SO2 and NO removal at the temperature range of 700-850 degrees C. The physical and chemical properties of the CaO sulfation products were analyzed to investigate the NO reduction mechanism. Experimental results showed that sulfated CaO had a catalytic effect on NO reduction by NH3 in the presence of excess O-2 after the sulfation reaction entered the transition control stage. with the increase of CaO sulfation extent in this stage, the activity for NO reduction first increased and then decreased, and the selectivity of NH3 for NO reduction to N-2 increased. The byproduct (NO2 and N2O) formation during NO reduction experiments was negligible. X-ray photoelectron spectroscopy (XPS) analysis showed that neither CaSO3 nor CaS was detected, indicating that the catalytic activity of NO reduction by NH3 in the presence of excess O-2 over sulfated CaO was originated from the CaSO4 product. These results revealed that simultaneous SO2 and NO, control by injecting NH3 into the dry flue gas desulfurization process for NO reduction might be achieved.