Several studies have shown the change of future river flow projection in the Chao Phraya River basin; however, these researches focused on the natural river flow. In this study, to obtain a realistic river flow projection for the Chao Phraya River basin, bias corrected GCM outputs were given to a regional distributed hydrological model including dam operation and flood inundation components. The projected river flow data was analyzed to assess the change of drought and flood risk. The GCM outputs used were precipitation and evapotranspiration projected by MRI-AGCM3.2S, which is a 20 km spatial resolution general circulation model developed by the Meteorological Research Institute, Japan Meteorological Agency. The results obtained from the projected river flow at the Nakhon Sawan station are as follows: 1) mean monthly discharge tends to increase in both the near-future and far-future projection periods for all months; 2) low-flow exceeding 99% of a mean daily flow duration curve for the near-future and far-future periods tends to decrease; and 3) a flood frequency analysis using the annual maximum daily flow series indicates that the flood risk in the near-future and far-future projection periods becomes higher.