The focus of this study is to estimate the daily actual evapotranspiration and assess itsrnspatio-temporal variability in Abaya-Chamo basin, southern section of the Main Ethiopian riftrnvalley using remote sensing techniques. The basin covers an area of 18,600 sq.km andrncomprises Abaya and Chamo lakes, and number of rivers and streams entering and leaving thernlakes. The daily actual evapotranspiration of the basin was estimated and thematically mappedrnon a pixel-by-pixel basis by applying Surface Energy Balance Algorithm for Land (SEBAL) modelrnon MODIS/Terra images acquired in six days between January and December 2006. SEBAL isrnan image processing model that uses spatially distributed spectral remote sensing data (visible,rnnear infrared and thermal infrared) to derive radiation, heat and evaporation fluxes. Wind speedrnand sunshine hour from standard metrological stations were used in modeling. The Evaporativernfraction in the land surface exhibited similar regional distribution patterns to the evaporation raternin the basin. In dry seasons, the average evaporative fraction did not exceed 0.4, highlighting therndominance of sensible heat flux across the basin, and the corresponding rise in observedrnsurface temperatures, whereas in wet seasons the EF reached a maximum value of 0.78. Thernresult of this study generally demonstrates that SEBAL could be used to provide information onrnevaporative loss and moisture condition of the water shade/catchment/basin during modelingrnprocesses because image record parameters integrated over a large area. The spatialrndistribution pattern of actual evapotranspiration is significantly affected by soil moisture contentrnand land use/cover pattern in the basin. In the rift, escarpment and highland, maximum dailyrnevapotranspiration from land surface was recorded in the wet autumn days followed by springrnand summer days. In winter days, the rift floor is usually dry and higher evapotranspirationrnvalues are limited to swamps/marshy areas. Unlike the rift, relatively high mean daily ETa valuesrnin the warm winter days are noted on the highlands. Comparative assessments of the result ofrnthis study with the results obtained from river discharge measurements are in good agreement,rnthe difference being less than 10%. But Thornthwaite type soil water balances over estimate ETarnby 17% to 37% from mean SEBAL results. This may be due to fracture systems that facilitaternwater loss in the area in which they do not have well representation in the model. The spatiallyrndistributed SEBAL ETa can be used to set water budgets for hydrological modeling, to supportrnwater planning, to estimate aquifer depletion and to support ground water modeling. These canrnbe most promising study area in the basin in the future. The integration of remote sensingrntechniques and distributed hydrological modeling can produce better results.rnKey words: actual evapotranspiration, lake Abaya-Chamo, MODIS/Terra, SEBAL