The paper presents results of three-year studies (2001–2003) upon evapotranspiration of grasses performed for grazing on peat-bog soil. The aim of the studies carried out in lysimeters was to evaluate water utilization for evapotranspiration of Lolium perenne, Phleum pratense and Poa pratensis depending on ground water level and mixture species composition. Grasses were sown in pure sowing and the following mixtures: Pp; Pp+Php; Php; Pp+Lp; Lp at two ground water levels (90 cm and 50 cm). The amount of water utilization by the sward of particular species and mixtures within 10-day periods was estimated on the basis of: useful precipitation, changes of soil profile retention, water poured in and poured out from lysimeters. Then, 10-day values of the real evapotranspiration values were calculated. The studies revealed that the amount of water utilized for real evapotranspiration of tested grasses was significantly differentiated depending on ground water level as well as the species composing a mixture. Significant differences were also recorded in particular cuts, which may prove the effect of weather and yield elements on evapotranspiration.