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An important consideration in designing and managing forage systems is the knowledge of the physiological response mechanisms to cutting, especially when water deficit conditions are prevailing. The objective of this study was to determine the physiological response of Medicago sativa and Festuca arundinacea to cutting under different water regimes in a semi-arid Mediterranean region. In a field experiment, two cutting intensities were applied under irrigation and under rainfed (water deficit) conditions. Water potential, transpiration rate and stomatal conductance were measured. Based on the results, M. sativa showed higher transpirational water losses under rainfed conditions when compared to those of F. arundinacea, regardless of cutting treatment, because of the higher stomatal conductance. However, leaf water potential remained higher in M. sativa, suggesting a more effective root, stem or leaf related water uptake system. In addition, under water deficit, stomata of M. sativa were less sensitive to low values of water potential, probably resulting in higher productivity when compared to F. arundinacea. Cutting resulted in higher stomatal conductance and, therefore, higher transpiration in both species. Moreover, under water deficit, cutting positively affected water potential, especially in F. arundinacea, alleviating the effect of ageing.