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Although the exhaust gas in a heavy-duty methanol engine is an oxygen rich atmosphere, there is some unburned methanol in the exhaust gas. Then, NOx control concept using lean NOx catalyst with unburned methanol as the reducing agent is considered. The purpose of this study is to verify the capability of lean NOx catalyst to reduce NOx in actual methanol engine exhaust. It was found through synthetic gas tests that alumina catalysts are effective for NOx removal. It was also found through engine tests that the catalyst temperature range between 500 °C and 600 °C and space velocity of less than 20,000 1/hr are requirements for a high NOx conversion efficiency. Although NOx conversion efficiency decreased at full load engine condition, it could substantially promote NOx conversion efficiency to add methanol into the exhaust gas before the catalyst bed.