Abstract: A heating system for a catalytic converter of a multi-cyclinder, spark-ignition engine is provided. Half of the cylinders of the engine, for example, the cylinder #2 and the cylinder #3, are operated on a rich gas mixture with an excess air ratio of 0.6 or less to produce a combustible gas mixture comprising hydrogen, carbon monoxide, and unburned fuel components, while the remaining half of the cylinders, for example, the cylinder #1 and the cylinder #4, are utilized as air blowers to which no fuel is fed. The flammable gas mixture produced from the combustible gas produced in the cylinder #2 and the cylinder #3 and the air supplied by the cylinder #1 and the cylinder #4 is burned in the combustor equipped with an ignition device which is installed upstream from the catalytic converter to provide heat energy to activate the catalyst. The system can rapidly heat and activate the catalyst without requiring a special fuel supply system and air blower.