The transport of the sediment, carried in suspension by water, is central to hydrology and the ecological functioning of river floodplains and deltas. River discharge estimation is useful for demonstrating this information. In this study, we extracted MODIS reflectance values from a pixel near the river mouth after carrying out the simple atmospheric correction method, then applied single regression analysis to reflectance values and the in situ discharge of Monobe River in Kochi prefecture, Japan. MODIS images and in situ data were taken from January through December, 2004. As a result, Monobe River, robustly positive relationships between the discharges observed in situ and remotely sensed MODIS reflectance data in the region of river mouth were found throughout the year. In addition, we estimated the monthly discharge from the MODIS reflectance with the regression formula. As a result, in situ average discharge was well estimated. In the near future, we will apply the proposed method to Mun river in Thai land.