The arid and semi-arid represent one third of the earth's surface. In these areas, soil salinity and irrigation water is one of the limiting factors for plant productivity and crop yields. These ecosystems are characterized by a high variability of rainfall combined with high evaporation favoring the accumulation of salts in the soil. This affects about 7% of the total area in the world. Germination of Medicago sativa is inhibited by 1.5% NaCl (260 mmol/l). Sodium chloride (NaCl) salinity is one of the major environmental factors that limit plant growth and productivity. In this study we tried to determine the effect of salt stress on germination of plants. For this, two alfalfa varieties were studied: Trifecta and Tafilalet that differ in their origins and their behavior to adapt to abiotic stress. Tafilalet ecotype from Morocco and Trifecta is a variety of Australian origin. To select the most tolerant alfalfa genotypes to salinity stress, an experiment was performed with three replications. The cultivar and salinity stress factors comprised two cultivars and tree levels of salinity stress (control, 100 and 200 mM) with NaCl, respectively. The all the results obtained showed that two genotypes contrasting for their sensitivity to salt stress exhibit behaviors that may differ in terms of response to salt stress, and indicate that a significant decrease was observed for mean germination in stress conditions.