Purpose <p>Salt stress severely retards plant growth, and melatonin has been demonstrated to have a significant effect in enhancing plant resilience to environmental stress. In order to study the effects of exogenous melatonin on the growth characteristics, photosynthesis and physiological function of chocolate mint under salt stress.</p> Methods <p>Various levels of melatonin (MT₁:100 µM, MT₂:200 µM, MT₃:300 µM) were administered to chocolate mints subjected to salt stress (320 mM NaCl) in the experiment.</p> Results <p>The results demonstrated that 200 µM melatonin increased the fresh weight, the dry weight, the water potential value of leaf, and net photosynthetic rate by 68.81%, 32.63%, 39.76% and 39.76% respectively in comparison to the salt-stress treatment alone (NaCl). Exogenous melatonin also significantly reduced the contents of soluble sugar, soluble protein, free proline, and the sodium-to-potassium ion ratio under salt stress, enhanced the activity of antioxidant enzymes and decreased the contents of malondialdehyde, hydrogen peroxide and electrolyte leakage level.</p> Conclusion <p>These results indicate that exogenous melatonin could regulate the content of osmotic substances, increase the activity of antioxidant enzymes, promote the removal of reactive oxygen species, and protect the cell membrane, thus reducing the inhibition of salt stress on plant growth. Among the tested concentrations, 200 µM emerged as the most effective dose for alleviating salt stress-induced damage in chocolate mint. This study confirmed the role of melatonin in enhancing the salt tolerance of chocolate peppermint, which provided reference for the conservation and management of peppermint, and also provided more plant choices for reclamation and utilization of saline land and agricultural production.</p>