An exhaust gas treatment system is provided that can sufficiently remove pollutants such as SO.sub.3 contained in combustion exhaust gas at low cost. In the exhaust gas treatment system for removing pollutants such as SO.sub.3 contained in combustion exhaust gas, there is provided dissolved salt aqueous solution sprays 35A, 35B, and 35C, that spray an Na.sub.2SO.sub.4 aqueous solution obtained from desulfurization effluent of a wet desulfurization system, into a flue though which the combustion exhaust gas flows.