Evapotranspiration (ET) monitoring has important implications on global and regional climate modelling. Accurate measurement and estimation of ET is a basic input to compute water balance and to estimate water availability and requirements. Most methods for ET computation can only provide point estimates of ET for a specific location, fails to provide ET on a regional scale and makes it inadequate for proper water resource management. Koga irrigation scheme, which is found in Northwest highlands of Ethiopia, has high potential for irrigation agriculture, hence, there is an increasing demand of water utilization and variability of the water distribution as the result irrigation water management issue raise from time to time. The objective of this research was to estimate the daily and seasonal evapotranspiration of koga irrigation scheme and mapping its distribution using the Surface Energy Balance Algorithm for Land (SEBAL Model), Landsat 8 satellite images from the month of December to April have been taken to estimates the instantaneous actual evapotranspiration. Then the evaporative fraction was estimated from the instantaneous actual evapotranspiration and extrapolated to the daily ET values. Finally, the seasonal ET is the cumulative ET from the daily ET using the evaporative fraction, which derived from the satellite images and the Penman Monteith reference evapotranspiration using ETo calculator software. The daily Penman-Monteith reference evapotranspiration ETo which calculated from meteorological data of the scheme was found as, 3.2, 3.5, 3.4, 4.5, and 4.5 mm/day at December2020, January 19, February 20, March 24 and April 09/2021 respectively. The actual evapotranspiration of the scheme computed using SEBAL model ranges from 2.18 to 2.23, 2.20 to 2.97, 2.35 to 3.22, 3.17 to 4.34 and 3.10 to 4.20 mm/day that observed on uncultivated lands and water bodies (night storages) of the scheme, respectively. The ETseason evapotranspiration of the scheme also measured between 254.649 to 347.025 mm depth of water.Finally, the daily SEBAL ET was compared to the Penman Monteith daily reference ET and the linear regression analysis shows that daily ET of the SEBAL model has a strong relationship with Penman-Monteith reference evapotranspiration using ETo calculator of the study area,Crop factor (Kc) for every growth stage taken from Allen et al (1998). Keywords: Evapotranspiration; Landsat 8;SEBAL Model; Koga irrigation scheme