We describe in this report an effort using the MIT/NCAR three-dimensional aerosol-climate model to study the impact of ship emissions on chemical composition and radiative forcing of aerosols. Our results indicate that international shipping can be a non-negligible factor in determining the radiative forcing of aerosols over specific regions with intensive ship activities. These places include the European, eastern Asian, and American coastal regions. The global mean aerosol radiative forcing caused by the ship emissions ranges from -12.5 to -23 mW/m2, depending on whether the mixing between black carbon and sulfate is included in the model. However, over the aforementioned places, the radiative forcing resulting from ship emissions can be much more important in the total regional aerosol forcing.