Abstract: A method for removing nitrogen oxides from combustion exhaust gases obtained after removing sulfur oxides by a wet process, which is characterized in that the gases obtained after removing sulfur oxides from the combustion exhaust gases by a wet process are introduced into a wet electrostatic precipitator to remove most of the impurities such as dusts, fumes and mists, passed through a dummy catalyst layer in the form of a fixed bed or a moving bed to remove the remaining impurities which is set before or after heating the gases to a temperature suitable for the reaction of reducing nitrogen oxides, and passed through a metal oxides catalyst layer in the form of a fixed bed in the presence of ammonia which is used at least in the stoichiometric amount required for reducing nitrogen oxides to nitrogen gas by which the gases containing nitrogen oxides are reduced to harmless gases.