5-aminolevulinic acid (ALA), a key biosynthetic precursor of tetrapyrroles, is vital for plants adaptation to abiotic stress. To verify the effects of different concentrations of ALA, we applied exogenous ALA with different concentrations (0, 5, 10, 15, 20, 25 mg·L^-1) to the leaves of Lycium ruthenicum seedlings subjected to 300 mmol·L^-1 NaCl. Then, the physiological and growth indexes of L. ruthenicum seedlings were determined, and comprehensively evaluated the salt tolerance of the seedlings under each treatments. Results revealed that: (1) compared with the control, the plant biomass, the contents of chlorophyll, carotenoid and soluble protein, the activity of POD were significantly decreased by 33.39%, 19.06%, 24.38%, 39.57% and 47.91% (P<0.05) in L. ruthenicum leaves under the salt stress, but the contents of proline (Pro) and malondialdehyde (MDA) were significantly increased by 165.74% and 49.16%, respectively. (2) When exogenous ALA and NaCl were treated at the same time, the contents of carotenoid and malondialdehyde (MDA), the activities of CAT, POD, the plant height and total biomass were restored to the control level, and the contents of chlorophyll and proline (Pro) were significantly increased compared with the control in L. ruthenicum seedlings. (3) The contents of carotenoid and proline, the activities of antioxidant enzymes and biomass of the leaves of L. ruthenicum seedlings performed a trend that first increased and then decreased with the add of ALA concentration. The evaluation by membership function analysis indicated that 15 mg·L^-1 ALA had the best effects on alleviating salt stress in L. ruthenicum seedlings under 300 mmol·L^-1 NaCl stress. These findings suggested that ALA of appropriate concentration can regulate photosynthesis and antioxidant enzyme activities of L. ruthenicum seedlings by promoting the accumulation of chlorophyll and heme, and increase the accumulation of proline in vivo, thus effectively alleviating the toxic effect of salt stress on plants and promoting plant growth.