Postharvest 'Ziniangxi' litchi fruit were used as experimental materials and dipped in 0.5 mmol/L melatonin (MT) solution for 10 min. After drying， the fruit was refrigerated at (4 ± 1) °C and (85 ± 5)% relative humidity for 30 d. During refrigeration， the effects of MT treatment on the chilling injury (CI) and its related physiological metabolism in litchi were investigated. The results showed that MT treatment reduced the chilling injury index and delayed the decrease in the chromaticity a* value in cold-stored litchi fruit. The CI index in MT-treated fruit was 49.4% lower than that in control fruit at 30 d， while chromaticity a* value in MT-treated fruit was 37.2 % on average higher than that in control fruit from 10 to 30 d of refrigeration. MT treatment significantly inhibited the increases in membrane relative conductivity while suppressing the accumulations of malondialdehyde (MDA)， superoxide anion (O₂·-) and hydrogen peroxide (H2O₂)， as shown by the decreases of 29.6%， 16.9%， 6.9% and 6.3% in relative conductivity， MDA content， O₂·- production rate and H2O₂ content in MT-treated fruit at 30 d， respectively， thus contributing to mitigation of oxidative stress and maintenance of membrane integrity. MT reduced the activities of polyphenol oxidase (PPO) and peroxidase (POD) as well as inhibited the decreases in total phenolics， flavonoids and anthocyanins contents in cold-stored litchi fruit， thereby ameliorating enzymatic browning. MT treatment significantly enhanced the activities of superoxide dismutase (SOD)， catalase(CAT)， ascorbate peroxidase(APX)， monodehydroascorbate reductase (MDHAR)， dehydroascorbate reductase (DHAR) and glutathione reductase (GR)， and maintained higher levels of ascorbic acid (AsA) and reduced glutathione (GSH) contents and the higher ratios of AsA/ dehydroascorbic acid (DHA) and GSH/ oxidizided glutathione (GSSG) when compared to control fruit， which could lead to increases in antioxidant activity in litchi fruit during cold storage. In addition， MT treatment up-regulated the expression abundance of LcMsrA1， LcMsrA2， LcMsrB1 and LcMsrB2 during cold storage， thereby promoting the improvement in repair capacity of oxidized protein. The results indicate that exogenous MT treatment could alleviate the CI occurrence in cold-stored litchi fruit by modulating the chilling tolerance-related physiological metabolisms.