Abstract: The effects of salt stress on antioxidant capacity and photosynthetic characteristics of Prunella vulgaris seedlings were studied to provide a theoretical understanding to aid cultivation and management, and the breeding of salt resistant varieties of P. vulgaris. P. vulgaris seedlings were incubated in nutrient solution, the seedlings were treated with NaCl concentrations of 0, 20, 40, 60 and 80 mmol/L. Antioxidant enzyme activities, osmolyte concentrations, chlorophyll content, and photosynthesis parameters were quantified after the treatment. The results showed that with increasing salt concentration, superoxide dismutase, ascorbate peroxidase, and soluble protein content increased with increasing salt concentration to 40 or 60 mmol/L and then decreased as concentration rose further; peroxidase, soluble sugar content, malondialdehyde content and electric conductivity showed a continuously rising trend; chlorophyll a and chlorophyll b, chlorophyll a/b, carotenoid and total chlorophyll declined with every increase in salt concentration, as did net photosynthetic rate, transpiration rate and stomatal conductance. Intercellular CO₂ concentration first decreased as NaCl concentration increased, with the lowest value at 60 mmol/L salt concentration and the highest at 80 mmol/L NaCl. The stomatal limit value steadily increased from 0.26 in CK to 0.38 in 60 mmol/L NaCl, and then decreased to 0.24 at 80 mmol/L. The decrease in net photosynthetic rate caused by 20-60 mmol/L NaCl stress was considered to be a result of stomatal restriction, the decrease of net photosynthetic rate caused by 80 mmol/L NaCl stress was mainly attributable to non-stomatal limitation. Under NaCl stress, P. vulgaris increased the activity of antioxidant enzymes and the contents of osmolytes, and thus increased salt stress tolerance.