The effects of water stress on some compatible solutes including proline, soluble sugars and glycine betaine, the level of lipid peroxidation and membrane stability in two species of Sainfoin (Onobrychis radiate (Desf.) M.Bieb. and Onobrychis viciifolia Scop.) were investigated. The experimental plan was a basic factorial design, completely random with four replications and water stress was applied based on irrigation at 50, 60, 70 and 100% of Field Capacity (FC). Different physiological responses were observed between the species in their response to water stress. Our results showed that O. radiata possessed greater increments in soluble sugars content and glycine betaine than O. viciifolia. The Relative Water Content (RWC) in O. viciifolia was significantly lower comparing with O. radiate. The Relative Water Loss (RWL) of O. viciifolia had significantly decreased compared to control plants in all treatments and O. viciifolia was not able to withstand the 50% soil field capacity and dried out. Lipid peroxidation in O. radiata was lower than O. viciifolia and membrane of leaf cells in O. radiata was more oxidatively stable compared to O. viciifolia.