Disclosed is an incombustible composition for a fire door/wall, the fire door/wall using the incombustible composition, and a method of producing the fire door/wall. The incombustible composition includes 1 to 80 wt % of organic or inorganic fiber, 1 to 80 wt % of fly ash or bottom ash, 1 to 80 wt % of fire-proofing agent, 1 to 30 wt % of curing fire-retardant resin, and 1 to 40 wt % of incombustible hollow filler. Furthermore, the method includes providing the incombustible composition, mixing the fly ash or bottom ash, fire-proofing agent, and curing fire-retardant resin with each other, adding the organic or inorganic fiber into a mixture, shattering the mixture containing the organic or inorganic fiber, mixing an incombustible hollow body with the shattered mixture by use of a mixer using air, pressing the resulting mixture using a high pressure hot press to form a board or a square timber, constructing a frame of the fire door/wall using the board and/or square timber, and embedding an incombustible core material into the fire door/wall. As well, 1 to 70 wt % of the incombustible composition may be made of a waste material. Accordingly, the incombustible composition is advantageous in that the production costs are reduced, and that it is useful as a construction finishing and interior material because no fire and toxic gases occur when the incombustible composition is on fire.