Abstract: This invention is an exothermic composition prepared by mixing an iron powder with a mixed fibrous and carbonaceous powder as impregnated with a solution prepared by dissolving a proper amount of a neutral salt in an aqueous solution of an alkali or alkaline weak acid salt so as to mature when left sealed and a warming bag wherein said exothermic composition is contained in a ventilative inner bag provided in a part with a group of ventilating holes and a nonventilative label covering it and this inner bag is contained in a nonventilative outer bag.