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Lawn was planted in three lysimeters as the refrence crop in order to adopt an accurate method CS) of estimation of potential evapotranspiration for reference crop in Isfahan. The daily evapotranspriatior of Lawn was measured in a water balance type lysimeter for two years. Furthermore, Climatalogical data were collected in a weather station in Isfahan Univetsity of technology and potential evapotranspiration was calculated using 12 different methods. Comparing calculated and measured values of reference crop potential evapotranspriration showed that the Jensen—Haise, Christiansen and Hargreaves, adgusted Blaney-Criddle, Penman and Turc methods give better estimates of reference crop potential evapotranspiration, respectively.