The Japan Gas Association has been engaged in the development of a 200-kW-class ceramic natural gas engine system to be used as a co-generation power source, subsidized by Ministry of International Trade and Industry. The engine has several new concepts to achieve high efficiency and low emissions simultaneously and to enable to use natural gas as fuel supplied with low pressure in spite of diesel engine. The co-generation system needs de-NOx system. So, we developed a urea de-NOx catalyst system for high-temperature exhaust gas. This paper will describe the result in the fiscal year 1998.