Disclosed is an incombustible composition, an incombustible construction product using the incombustible composition, and a method of producing the incombustible construction product. 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, and 1 to 60 wt % of fire-retardant curing agent. Additionally, the method includes mixing components, constituting the incombustible composition, with each other, and shaping the incombustible composition using a roller press or an autoclave. Therefore, the incombustible composition is advantageous in that it is environmentally-friendly because it contains waste materials, and that it has excellent hardness, strength, and water resistance. Other advantages are that its production costs are relatively low, and that it has excellent incombustibility, depending on the contents of the components constituting the incombustible composition.