Salt-alkali stress is a major environmental factor that seriously limits crops development and productivity worldwide. The objective of this study is to compare growth and physiological responses of sainfoin (Onobrychis viciaefolia) to alkali (NaHCO₃) and salt-alkali (NaCl: NaHCO₃) stress, by investigating biomass, photosynthetic pigments, antioxidant enzymes, inorganic ions, organic substances such as proline and sugars. It was shown that both alkaline and saline-alkaline stress treatments significantly reduced fresh weight (FW) and dry weight (DW), chlorophyll (Chl) contents, K⁺ concentrations, antioxidant enzymes activity and soluble sugars contents, whereas clearly increased malondialdehyde (MDA), proline and Na⁺ concentrations in sainfoin plants compared with control (no added NaCl and NaHCO₃). It is also observed that in the 150 mM NaHCO₃, peroxidase (POD) activity, soluble sugar contents and K⁺/Na⁺ ratio in plants under NaHCO₃ treatment were lower than those in plants under NaCl: NaHCO₃ treatment. These results suggested that the damages caused by alkaline stress on the growth of sainfoin plants are more serious than those caused by saline-alkaline stress treatments. The findings of the present work provide a basis for understanding the physiological responses to saline-alkaline stress in forage legumes.