Abstract: To investigate the effects of exogenous melatonin treatment on browning and reactive oxygen species metabolism of Postharvest litchi, "Feizixiao" litchi was used as the material in this study. Litchi was treated with clear water and exogenous melatonin at different concentrations(50, 100, 200 μmol/L), and the relevant physiological indexes related with active oxygen metabolism were determinated at regular time during storage at 4℃. The results showed that different concentrations of melatonin could reduce the weight loss rate, browning index and cell membrane permeability of litchi, maintain the original color(L^*: brightness), reduce the production rate of superoxide anion(O₂^-) and the activity of polyphenol oxidase(PPO), slow down the production and accumulation of MDA and hydrogen peroxide(H₂O₂), improve the activity of SOD and maintain the integrity of cell membrane of litchi fruit. In particular, 50 μmol/L melatonin treatment showed the best effect. It could be speculated that melatonin treatment can delay the aging process of postharvest litchi by regulating its reactive oxygen species metabolism, which provides theoretical support for melatonin application and postharvest preservation of Litchi.