To select rabbiteye blueberry leaves from an appropriate harvest season to develop functional foods, this paper studied the bioactive secondary metabolites and the antioxidant capacity of rabbiteye blueberry leaves from May, September, and November. The results showed the leaves from May had the highest content of total flavonoids (114.21 mg/g) and the leaves from November had the highest content of total polyphenols and proanthocyanidins (425.24 and 243.29 mg/g, respectively). It was further found that blueberry leaves from different seasons have similar bioactive constituents, but their contents are obviously different by HPLC. The rabbiteye blueberry leaves from November had the highest antioxidant capacity, which was well correlated with their highest proanthocyanidin content. The results clarify that the blueberry leaves from different seasons have different contents of bioactive secondary metabolites and different antioxidant activities, which implied that leaves from November should be selected first for utilization in functional foods.