The purpose of this study was to assess the hydrological roles of the Cambodian floodplain of the Mekong River, from Kompong Cham as far south as the Vietnam border. An intensive observation of water levels at 20 locations, discharge measurements by ADP and ADCP in the main/floodplain channels and analysis of satellite images (RADARSAT) to estimate inundated area and storage volume, were carried out during the flood and post flood season in 2002. A hydro-hydraulic model was set up for the entire study area to establish a tool for assistance in understanding the dynamics of recurrent floods as well as the hydrological roles of the floodplain in Cambodia. The model system used was MIKE11, a generalized one-dimensional model system for rivers and estuaries. The hydraulic modeling work enabled us to assess the hydrological roles of the study area. The flood reduction amount in the peak flood season and river flow augmentation in the dry season were determined as part of the study. The main findings are of importance to floodplain management, as future construction for example for improved road levees and higher agricultural dykes, may reduce the benefits presently derived from flows over the floodplains. The work was carried out under the MRC (Mekong River Commission) Project named Consolidation of hydro-meteorological data and multi-functional hydrological roles of Tonle Sap Lake and its vicinities.