Abstract: The aims of this study were to evaluate the physiological responses of quinoa plants to salt stress and to compare salt tolerance among different quinoa varieties. Seeds and seedlings of different quinoa varieties were pretreated with 100, 200, 300, 400, and 500 mmol/L NaCl solutions. The seed germination index, seedling biomass, and other physiological and biochemical characteristics were determined to analyze the mechanisms of salt tolerance in quinoa. The salt tolerance of the different quinoa varieties was evaluated by a membership function method. As the NaCl concentration increased, the seed germination percentage increased and then decreased, the germination potential and germination index decreased significantly, and the contents of chlorophyll and soluble proteins and activities of antioxidant enzymes (superoxide dismutase, peroxidase, catalase, and ascorbate peroxidase) increased and then decreased. The peak in the activities of the antioxidant enzymes was at 300 mmol/L NaCl. The contents of soluble sugars, proline, and malondialdehyde increased significantly as the NaCl concentration increased. These results suggested that increased contents of soluble sugars and proline, increased activities of antioxidant enzymes, and decreased malondialdehyde contents in seedlings may contribute to adaptation to salt stress and promote seedling growth in the presence of NaCl. In conclusion, the threshold of salt tolerance in quinoa seedlings was 300 mmol/L NaCl. Longli No.1 was the most salt-tolerant quinoa variety, and Longli No.4 was the least salt-tolerant variety.