According to revisions of survey law taking effect on January 1, 2003, the Korean geodetic datum has been changed from a local geodetic to a world geodetic system. Since the datum change demands a geographical data transformation, the National Geographic Information Institute has established step-by-step plans for the transformation of the land data constructed through the National GIS Project, and it is in progress. For maritime data, however, no detailed transformation plan has been established yet. Therefore, it is necessary to analyze the maritime geographic data obtained through the Maritime GIS project and set up the data transformation scheme to a world geodetic system. In this study, the datum transformation parameters especially for the maritime geographical data are determined. From database constructed through MGIS, a total of 492 coordinate pairs were used in parameter determination initially. At this stage, three popular seven parameter transformation models, Bursa-Wolf, Molodensky and Veis model, and the multi regression equation are applied, and the transformation parameters from the Molodensky model are selected for its accuracy and consistency with the land data transformation method. To eliminate the local bias caused by the nonequally distributed stations, a network optimization is applied and 42 stations are selected to determine the final transformation parameters. The distortion after applying the similarity transformation is modeled through a least squares collocation with Gaussian model, and high accuracy better than 15 cm in coordinate transformation is obtained.