An object of the present invention is to provide a treatment agent superior in harm-removing performance to metal hydride containing exhaust gas, and its production method as well as a treatment method. It is a mixture of either copper hydroxide or basic copper carbonate and silicon compound or a mixture, wherein parts of said copper compound and said silicon compound form a complex. A preparation of the treatment agent is made by a precipitation method, wherein a copper salts solution serves as a precipitation mother solution, and a mixture solution of either alkali hydroxide or alkali carbonate and alkali silicate serves as a precipitating agent. A treatment agent obtained as its result shows a high harm-removing performance to the metal hydride gas and a low heat generation, for which reason the agent is useful for treatment of the metal hydride containing exhaust gas generated in semiconductor manufacturing.