In order to grasp the process of hydrologic cycle in river basin, it is necessary to estimate the evapotranspiration correctly. But, it is difficult to observe the meteorological data for the evapotranspiration, because of the extent of observation area. The purpose of this work is to determine the ratio of actual evapotranspiration and potential one in each land use to estimate the actual evapotranspiration from the potential one which can be calculated easily. I carried out the observations of actual evapotranspiration at the Bibi swamp experimental station and the Komasato grassland to determine the ratio of paddy and grassland area. In this study, the actual evapotranspiration are calculated by the profile method at the Bibi site, the Bowen ratio method at the Komasato site, the potential one are calculated by penman method. The ratio of forest area are determine using the evapotranspiration from water balance method.