AN ACCURATE DETERMINATION OF EVAPOTRANSPIRATION IS REQUIRED FOR MANY STUDIES THAT INVOLVE ESTIMATION OF THE WATER BALANCE. ONE METHODOLOGY IS THE USE OF LysimeterS CONSIDERING THE SEMIARID CLIMATE OF KERMANSHAH PROVINCE, IN THE PARTS OF IRAN. THE LysimeterIC DATA WERE USED FOR THE EVALUATION OF NINE GRASS EVAPOTRANSPIRATION MODELS, INCLUDING FAO-56 PENMAN–MONTEITH, PENMAN-KIMBERLY 1996, FAO-PENMAN EQUATION, BLANEY–CRIDDLE, FAO-24 RADIATION, MAKKINK, TURC, PRIESTLEY–TAYLOR, AND HARGREAVES. FINALLY, THE RESULTS SHOWED THAT THE MODEL OF FAO-56 PENMAN–MONTEITH, TURC AND MAKIN WERE THE BEST MODELS FOR THE INVESTIGATED REGION. FOR COMPARISON OF DIFFERENT EVAPOTRANSPIRATION ESTIMATION METHODS DIFFERENT STATISTICS PARAMETERS SUCH AS RMSE, MBE, R AND T WERE USED. THE RESULTS SHOWED THAT THE BEST PRECISE ARRANGEMENT METHOD IN THE REGION WERE FAO-56 PENMAN–MONTEITH, TURC, MAKKINK, PRIESTLEY AND TAYLOR, HARGREAVES,BLANEY-CRIDDLE RESPECTIVELY. AMONG THESE NINE METHODS, FAO-RADIATION, FAO-PENMAN EQUATION AND PENMAN-KIMBERLY RANKED AS THE LAST THREE, AND PENMAN-KIMBERLY CANNOT BE RECOMMENDED.