An object of the present invention is to provide a method for removing gaseous mercury in flue gas that make it possible to remove mercury in flue gas extremely satisfactorily while handling is made easy and cost increases are kept under control. In order to accomplish the object, the present invention adopts the method of removing gaseous mercury in flue gas, in which, after water-insoluble mercury in the flue gas is converted into water-soluble mercury by placing the flue gas in contact with a solid catalyst formed by a metal oxide, wet-type absorption is performed on the water-soluble mercury.