This paper describes NOx and COx emissions from the diesel engine on mini-vessel such as 500GT class vessel under transient operating condition and entering and departing conditions, because the reduction of the marine exhaust emissions has been important subject. And the International Maritime Organization (IMO) advances the prevention of air pollution from ships in 1989. The regulated level of NOx emissions will be decided by the Bulk Chemicals (BCH), in recent years. So the emissions of carbon monoxide (CO), carbon dioxide (CO2), total hydrocarbons (THC), sulfur dioxide (SO2), and nitrogen oxide (NOx), occupy an important part. The transient operating conditions have been formed by change of engine speed and PPA whose region are within the range of 500-673rpm, and 11-20deg. NOx concentration in summer voyage changes within the limits of 600- 1000ppm, and CO2concentration changes within the limits of 4-7%.