Background: Diospyros melanoxylon Roxb. belongs to the family Ebenaceae and its leaves show diuretic, carminative, laxative, and styptic bioactivities. Objective: The objective of this study was to give a direction for future investigators to carry out research on phytochemistry and develop a potent antidiabetic agent. Materials and Methods: Petroleum ether extract of D. melanoxylon Roxb. leaves was chromatographed over silica gel column. Isolated compounds were elucidated on the basis of different spectroscopic techniques (mass spectrometry, infrared, 1H, 13C nuclear magnetic resonance, and distortionless enhancement by polarization transfer). Antidiabetic activity of lup-20 (29)-ene-3α,6 β-diol was evaluated in streptozotocin diabetic rats. Results: A novel compound, lup-20 (29)-ene-3α,6 β-diol (6), was identified along with 11 known natural compounds, namely, lupeol (1), ceryl alcohol (2), octacosanol-1 (3), hentriacontanol-1 (4), β-sitosterol (5), diospyrin (7), 3α-methoxydiospyrin (8), betulin (9), ursolic acid (10), betulinic acid (11), and oleanolic acid (12). Further administration of lup-20 (29)-ene-3α,6 β-diol significantly improved the diabetes-induced oxidative stress. Conclusion: Investigation of this novel compound plays an important role in the field of drug development.