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Sixteen alfalfa cultivars originating from the Mediterranean basin were tested in an experimental station in Morocco, located in the semi arid bioclimatic area. This research was conducted in PERMED project during 2006-2008 and aimed to evaluate the adaptation of cultivars to drought stress. The trial was conducted under two irrigation treatments. The first treatment was normally irrigated by providing an amount of water corresponding to the potential evapotranspiration of the crop and in the second treatment with water deficit which was applied by stopping the irrigation during 9 weeks in summer. Results showed that water stress during summer significantly reduced aerial biomass of all cultivars. This reduction varied between 25 and 41% according to cultivars in comparison with a normal irrigated treatment. The difference between cultivars for biomass production was significant only in stress treatment (P<0.001 with 15 df). Some cultivars showed high forage yield potential, mainly Ameristand, ABT 805, Sardi10, Siriver, Gabes-2355, Rich2, and Erfoud 1 even in presence of stress. In the end of August (before restart of irrigation for treatment with suspended summer irrigation), the mean rate of leaf senescence of cultivars was 84% with no significant difference between cultivars. The row cover estimated in the end of summer of the third year varied between 12 and 40% according to the cultivars. Cultivars Gabes-2355, Ameristand and ABT805 showed a smaller number of dead plants under water stress. Therefore, those cultivars could be used by local farmers in this region.