Abstract: Taking the Ulmus pumila seedlings from three different habitats (medium-, mild-, and non-saline soils) as test materials, an experiment was conducted to study their salt-tolerance thresholds and physiological characteristic under different levels (0, 2, 4, 6, 8, and 10 g·kg^-1) of salt stress. With increasing level of the salt stress, theseedlings taken from medium and mild- saline habitats had a lower increment of leaf membrane permeability, Na⁺ content, and Na⁺/K⁺ but a higher increment of leaf proline, soluble sugar, and K⁺ contents, and a lower decrement of leaf starch content, net photosynthetic rate, transpiration rate, intercellular CO₂ concentration, and stomatic conductance, as compared with the seedlings taken from nonsaline habitat. The salttolerance thresholds of the seedlings taken from different habitats were in the order of medium saline habitat (7.76 g·kg^-1) > mild- saline habitat (7.37 g·kg^-1) > non-saline habitat (6.95 g·kg^-1). It was suggested that the U. pumilaseedlings in medium- and mild-saline habitats had a stronger adaptability to saline soil environment than theU. pumilaseedlingsin non-saline soil environment.