There are provided a heat-generating composition excellent in moldability, shape retaining property and heat-generating characteristics, and a heat-generating body using the same that can maintain theshape of a molded article of the heat-generating composition irrespective to the pressure inside the container bag and has excellent heat-generating characteristics and long-term heat generation maintaining property. It is a non-viscous heat-generating composition having excessive water characterized in that the heat generating composition generating heat in contact with air comprises, as essential components, a water absorbing polymer, a carbon component, a heat-generating promoter, water and a heat-generating substance, has excessive water, and has an incremental degree of viscosity of lessthan 1,000 cP and a liquid permeation degree of 5 or more.