To investigate the effect of exogenous melatonin on heat tolerance in kiwifruit seedlings under high temperature stress, we used the potted seedlings of Actinidia deliciosa cv. Qinmei as materials pretreated with melatonin solution by root irrigating, then under 45 ℃ heat treatment to determine the physiological indexes of resistance. Results showed that： (1) melatonin pretreatment significantly reduced the relative electrical conductivity level and malondialdehyde content in the leaves of the kiwifruit seedling, and significantly increased the proline content, catalase activity and peroxidase activity when compared with high temperature control. And the best effect was observed when the concentration of melatonin solution was at 100~200 μmol·L^-1. (2) Melatonin pretreatment significantly increased the contents of total phenols, total flavonoids and total flavanols, and improved antioxidant capacity assayed by three methods (ABTS, FRAP, DPPH). In summary, melatonin can improve the antioxidant capacity of plants by increasing the contents of phenols and flavonoids, so as to effectively alleviate the damage of high temperature to kiwi seedlings and improve the heat resistance.