One of the most important section for increasing water productivity and management is aware of the crop water requirement and calculation of evapotranspiration. Because of the importance of water’s problem in agriculture, the exact calculation of crop water requirement for variety of cultivated crops is necessary. Water requirement of most crops has been reported by FAO, but water requirement of many medicinal plants, increasing cultivation area of them in Iran, has not been studied. One of the methods used to determine crop water requirements if the input and output water in the system can be measured are water balance method by using lysimeter. This study aimed to measure water requirement of European borage has done by using lysimeter. In this way, seed of European borage were planted within a lysimeter placed in a field of European borage and under natural conditions in the Guilan Research Center for Agriculture and Natural Resources. The incoming and outgoing water of lysimeter were measured. Reference evapotranspiration was calculated using meteorological data from synoptic stations of Rasht Center and CropWat software using Penman-Monteith method. Then crop coefficient of borage in the growth period of the plant was calculated from the ratio of borage evapotranspiration and calculated ET0. The results showed that water requirement of European borage in the initial, the middle and the end stages are 0.66, 1.35 and 1.23 mm/day, respectively and crop coefficients of European borage are 0.2075, 0.3403 and 0.29, respectively.