Abstract: In order to study the alleviating effect and mechanism of exogenous proline treatment on Cinnamomum septentrionale seedlings under alkali stress, the 1-year-old seedlings of C. septentrionale under the treatment of 150 mmol/L Na₂CO₃, exogenous proline solution was sprayed for 14 days, and then the content of chlorophyll, chlorophyll fluorescence parameters, osmotic adjustment ability and antioxidation ability of plant leaves were measured. The results showed that the relative conductivity and MDA content of C. septentrionale seedlings under alkali stress are decreased significantly with the appropriate concentration of exogenous proline treatment, and the chlorophyll content, F_o, F_m, F_v/F_m, q_N, q_P, the contents of soluble sugar, soluble protein, malic acid and proline were increased, the activities of SOD, POD, CAT and total antioxidant capacity were increased, and the activities of PAL were decreased. The contents of MDA, F_v/F_m, F_o, F_m, q_N, SOD, POD and soluble sugar of C. septentrionale seedlings under alkali stress were significantly decreased by high concentration of proline, there were no significant differences in chlorophyll content, q_P, soluble protein content, proline content, malic acid content, CAT activity, total antioxidant capacity and PAL activity between the 2 groups, the maximum value of D reached 0.917 at 150 mmol/L. To conclud, exogenous 150 mmol/L proline can alleviate alkali stress of C. septentrionale seedlings and amalic acid may play an important role