Abstract: In order to explore the tolerant mechanism of two species of Lycium to NaHCO₃ stress, the responses of osmotic regulation and antioxidant systems to NaHCO₃ stress in Lycium dasystemum and Lycium chinense were investigated by determining the dry weight, the electrolyte leakage, the contents of malondialdehyde(MDA), H₂O₂, proline, Na⁺ and K⁺ as well as the activities of antioxidant enzymes like superoxide dismutase(SOD), catalase(CAT), peroxidase(POD), ascorbate peroxidase(APX)and glutathione reductase(GR). The results showed that growth of two Lycium species were improved under lower stress intensity as compared to that of control. The contents of Na⁺ and proline in leaves increased with the stress intensity increasing, while that of K⁺ decreased. The less oxidative damage of Lycium dasystemum was associated with lower MDA content, electrolyte leakage, and H₂O₂ concentration. With the increasing stress intensity, the activity of SOD increased, while that of CAT decreased gradually. The activities of APX and GR changed identically, which increased under lower NaHCO₃ stress, and then began to decrease under severer NaHCO₃ stress. These results presented that Lycium dasystemum exhibited a better protection mechanism against oxidative damage and it was more salt-tolerant than Lycium chinense possibly by maintaining better capability in osmotic regulation and a more effective antioxidant defense system.