Nitric oxide was effectively reduced by ethanol over an alumina-supported silver catalyst in the presence of excess oxygen and water vapor. In this reduction, though NO was mainly converted to N-2, there was also a substantial amount of nitrogen-containing by-products such as N2O, NH3, CH3CN, HCN. There was also a very small amount of by-products - HNCO and NH4OCN (and/or urea, an isomer). The effects of silver content of the catalysts, water vapor, space velocity, and ethanol concentration on the reduction of NO were studied. The mechanism for the formation of nitrogen-containing compounds was also examined on the basis of the reactions of model compounds and the analyses of the products.