Abstract: A heat generating agent for medical waste sterilization. The agent is at least one compound selected from calcium oxide, calcined dolomite, and magnesium oxide, and at least one compound selected from sulfamic acid, sodium bisulfate, and anhydrous phosphoric acid. The present invention also provides a method for sterilizing medical wastes. The method includes the steps of subjecting medical waste to exothermic reaction between water and a heat generating agent selected from calcium oxide and calcined dolomite or to exothermic reaction between iron powder and oxygen to generate reaction heat and/or alkalinity by the exothermic reaction. The present invention provides an aparatus to be used according to the method mentioned above.