Objective: To compare the physiologically active substances, antioxidant and antidiabetic activities in vitro of bitter melon fruit and leaf extract. Methods: Total polyphenol and flavonoid contents were measured using spectrophotometrically by gallic acid and catechin standard curves, respectively. The radical-scavenging potential of bitter melon fruit and leaf extract were measured by DPPH, ABTS and hydroxyl radical scavenging ability and reducing power and anti-diabetic ability was evaluated by α-glucosidase activity. Results: It was confirmed that the bitter melon leaf contained more total polyphenols and flavonoids than bitter melon fruits. Bitter melon leaf extract contained 2.8-fold and 4.9-fold higher total polyphenols and flavonoids than bitter melon fruits, respectively. The DPPH radical scavenging activity of bitter melon leaf was 5.81- and 5.70-fold higher than that of the bitter melon frui, based on 200 μg/mL and 400 μg/mL of the extract, respectively. In ABTS, hydroxyl radical scavenging ability and reducing power, the bitter melon leaf extract all showed higher antioxidant capacity than the bitter melon fruit. Bitter melon fruit showed 2.52- and 2.63-fold higher α-glucosidase inhibitory activity than bitter melon leaf extract at 200 μg/mL and 400 μg/mL, respectively.Conclusions: Based on our results, bitter melon may improve antidiabetic effects by upreguating α-glycosidase activity. Even, bitter melon leaf extract shows higher antioxidant potential than its fruit but bitter melon leaf extract does not show higher α-glucosidase inhibitory potential than bitter melon fruit. The overall results support that bitter melon fruit and leaf may have specific target effects on antidiabetic and antioxidant, respectively.