ABSTRACT A new xanthone: mangostanaxanthone VIIII [1,3,5,6,7-pentahydroxy-2-(3-methylbut-2-enyl)-8-(3-hydroxy-3-methylbut-1-enyl) xanthone] (5) and four known xanthones: mangostanaxanthones I (1) and II (2), γ-mangostin (3), and mangostanaxanthone VII (4) were separated and characterized from the acetone fraction of Garcinia mangostana L., Clusiaceae (mangosteen) pericarps. Their structures were established based on various spectroscopic analyses in addition to HRMS and comparison with the literature. The α-amylase inhibitory potential of the isolated metabolites was evaluated. Compounds 1, 2, and 5 had the highest activity with % inhibition 72.5, 86.5, and 81.8, respectively compared to acarbose (97.1%, reference α-amylase inhibitor). The molecular docking study of the tested metabolites was estimated to shade up the rational explanation of the α-amylase inhibitory activity results. Moreover, the pharmacokinetic parameters were assessed using Swiss ADME. It is noteworthy that 1, 2, and 5 had similar binding poses as the X-ray crystal structure of acarbose, whereas the other metabolites possessed different binding mode that decreased their inhibitory capacity. Thus, these data reinforced the health benefit of mangosteen as an alternative medicine to help lowering the postprandial glucose absorption. Therefore, it could have a good potential for the treatment of diabetes.