Abstract: Nitrous oxide contained in a gas is directly decomposed by contacting the gas with a catalyst layer composed mainly of tin (IV) oxide at a reaction temperature of not less than 250.degree. C., preferably not less than 300.degree. C. Particularly when a cobalt (II) compound is added to the catalyst layer, nitrous oxide can be effectively removed to a low concentration by contacting the gas with the catalyst layer at the reaction temperature of not less than 200.degree. C., preferably not less than 300.degree. C. By the present process, nitrous oxide which has not conventionally effectively removed can be reliably removed at a low cost. The present process can be applied for the removal of nitrous oxide in exhaust gases discharged from a sludge-incinerating furnace, a boiler fine powder coal combustion furnace, etc.