This research has been carried out to verify the performance of a charge air moisturizer system which was developed to reduce NOX emission from marine 4-stroke diesel engine, to comply with US EPA (Environmental Protection Agency) Tier II (Category 2) emission regulation. The charge air moisturizer system abates NOX emission from a diesel engine through supplying high level of humid charge air into a combustion chamber. As a result, NOX and THC (Total Hydro-Carbon) emissions met the EPA Tier II regulations, and PM (Particulate Matter) emission also met the regulations on the condition of MGO (Marine Gas Oil) or low sulfur fuel oil usage. But, the SFOC (Specific Fuel Oil Consumption) increased slightly. Performance test using this system did not leave any trace of rust, corrosion, abnormal wear, etc., on the inner parts of the engine. Thus, it can be concluded that the Charge Air Moisturizer system has little effect on the durability or reliability of engine components.