To investigate the effect of exogenous melatonin on postharvest black spot disease of apricot fruit. Using Xinjiang 'Saimaiti' apricot as test material， the sample were vacuum impregnated into different concentrations of melatonin (50， 100， 200 μmol/L) under pressure of 0.05 MPa for 2 min， then atmospheric pressure was restored， and the sample was maintained in the impregnation solution for 8 min， distilled water treatment was used as the control group， naturally dried， and then stored at (0±1) ℃ and 90%-95% relative humidity for 48 h， all samples inoculated with Alternaria alternata， and stored under the same conditions. The lesion diameter and disease incidence of apricot fruits， and the activities of phenylalanine ammonia-lyase (PAL)， cinnamic acid-4-hydroxylase(C4H)， 4-coumaric acid CoA ligase (4CL)， polyphenol oxidase (PPO) and cinnamyl alcohol dehydrogenase(CAD)， and the total phenolic， lignin and flavonoid contents were measured regularly. The results showed that exogenous melatonin treatment significantly reduced the lesion diameter and disease incidence of apricot fruits. On day 42 of storage， the diameters of lesions in different melatonin treatment groups (50， 100， 200 μmol/L) were 8.41， 7.20 mm and 8.01 mm， respectively， which were 5.68%， 19.32% and 9.45% lower than those in the control group (P<0.05)， and the inoculation incidence was 10.00%， 21.11% and 12.22% lower than that of the control group(P<0.05)， respectively， and 100 μmol/L melatonin treatment group inhibited the growth of Alternaria alternatas best. Melatonin treatment increased the enzyme activities of PAL， C4H， 4CL， PPO， and CAD and promoted the accumulation of total phenol， flavonoid， and lignin contents in apricot fruit. At the end of storage， the activities of PAL， C4H， 4CL， PPO and CAD of the melatonin-treated group were 400.75， 0.95， 0.48， 0.52， and 0.61 U， respectively， which were 15.18%， 41.04%， 18.51%， 15.63%， and 65.04% higher than those in the control group (P<0.05)， and the total phenol， flavonoid， and lignin contents of melatonin group were 1.10， 1.22， and 1.30 times higher than those of the control group(P<0.05). Those findings suggested that exogenous melatonin could regulate phenylpropanoid metabolism to improved the resistance of apricot fruits to the black spot disease.