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Exactly estimating of water requirement is essential for water balance studies, design and management of irrigation systems and water resources management. Because of limited soil and water resources in Iran, for optimal use of water resources in the agricultural sector, it is necessary to determine the amount of water requirement by different plants in different climatological conditions. In order to determine the water requirement and crop coefficients of Stevia, six lysimeter numbers were used in three replications for stevia and reference plant (grass). The reference Stevia plant evapotranspiration was measured on a daily basis. The results showed that during the 537 day period of Stevia cultivation, the maximum and minimum water requirement in the first and second year of cultivation was respectively 9.85 and 1.69 mm per day, and for the reference plant was obtained as 6.54 and 1.84 mm per day. In this study, the Kc coefficients in initial, development, intermediate and final stages of growth in 2016 were 0.76, 1.11, 1.46 and 1.05 and in 2017 at growth stages, were 0.76, 1.18, 1.52 and 1.29 respectively. The average of individual Stevia plant growth factors for four growth stages in two years of research was obtained as 0.76, 1.15, 1.49, and 1.17, respectively. [ABSTRACT FROM AUTHOR]