A method for disassembling a boiler supported and suspended by a supporting structure which includes the steps of cutting off a lower part of a furnace unit to provide an enlarged opening; fixing a first support to the furnace unit at approximately same height as a lower end of a heat recovery area; fixing a second support to the lower end of the heat recovery area; providing a first jacking apparatus and a second jacking apparatus under the first support and the second support, respectively; detaching the boiler from the suspending structure; lowering the first support and the second support by the first jacking apparatus and the second jacking apparatus, cutting a lower part of the boiler, repeating the lowering and the disassembling steps until the first support and the second support are lowered to a maximum extent; and disassembling a remaining upper part of the boiler.