Abstract:To explore the effects of exogenous melatonin （MT）on the quality of post-harvested litchi，"Fei Zi Xiao" litchi were soaked with 0.4 mmol/L of MT.As the control group，some samples were also treated with purified water.The litchis were stored at 4℃，and the changes in physiological indices were measured regularly.The results showed that during 16 days of the storage，the weight loss rate，browning index，relative electrical conductivity，O2-generation rate，malondialdehyde levels，and peroxidase activity of the melatonin treatment group decreased by 27.65%，29.39%，20.28%，19.65%,15.59%，and 14.77%，respectively，compared to the corresponding values of the control group.The L*value，anthocyanin content，catalase （CAT）activity，and superoxide dismutase activity of the melatonin treatment group were 8.24%，93.00%，44.42%，and 23.46% higher than those in the control group，respectively.In addition，the rate of increase in polyphenol oxidase activity in the melatonin treatment group was lower than that of the control group in the middle of storage.According to the principal component analysis，the contribution rates of the first and second principal components were 67.431% and 16.530%，respectively，and the cumulative total contribution rates were 83.961%.Weight loss rate and the CAT activity were the key indices used to evaluate litchi physiological quality.Melatonin could significantly delay the increase in weight loss rate and improve the CAT activity.