PURPOSE: A heat generation composition for disposal body warmer, etc., having a large amount of water retention, low viscosity during retention of water, and long duration time of given temperature, containing a diatomaceous shell having rough particle size as a water retaining material as well as a metal, its reaction auxiliary, water, etc.

CONSTITUTION: In a heat generation composition containing a metal such as iron, copper, etc. and its reaction auxiliary (e.g., potassium chloride, manganese dioxide, etc.), generating heat in the presence of water and air, a diatomaceous shell having slightly rough particle size (the residue of 100 meshes is preferably 10W30%) is used as a water retaining material. A calcined diatomaceous shell is preferable as the diatomaceous shell.