This study compared the antioxidant activity and functional constituents of the peel, flesh,and placenta of oriental melons according to the harvest time. The sample oriental melons were harvested during the major harvest time (from June to August) and divided into peel, flesh, and placenta. To examine the antioxidant activity and functional constituents, the sample melons were extracted using EtOH. As a result, the functional constituents and antioxidant activity of the oriental melons were found to change according to the harvest time. The total phenol and total flavonoid contents were highest in the samples harvested in June, and lowest in the samples harvested in July. Meanwhile, the antioxidant activities were estimated using an ABTS and FRAP assay, where the samples harvested in June also showed the strongest the antioxidant potential, while the samples harvested in July showed significantly lower antioxidant activities. This means that the climate influences the synthesis of secondary metabolites. The above data also suggests that oriental melons harvested in June contain more functional phytochemicals, making them more beneficial for human health.