We analyzed effects of evapotranspiration d stribution streamflow in a forested catch ment using a lumping model. The model was developed to understand the interrelation between components of water budget in two zones, source zone and hillslope zone. In this study, hydrological observations of precipitation, stream discharge, and soil moisture were conducted in a granitic steep headwater catchment inEtajima experimental forests, Hiroshima, Japan. We found a significant correlation between baseflow and saturation ofsource area. We analyzed effects of evapotranspiration on stand conditions onbaseflow by changing the transpi ration rate of each zone in the model. The results howed that (i) the annual trend of baseflow was strongly affected by evapotranspiration of the upper hillslope and (ii) the effects ofevapo transpiration f source zone on baseflow appeared only during the dry period. We conclude that it is important toestimate each stand type of evapotranspiration and its distribution for under standing baseflow generation i the steep forested catchments.