The present study was designed to identify the ability of the leaf extract from Syzygium malaccense (L.) Merr. L.M. Perry to scavenge DPPH, ABTS and NO radicals; to inhibit the carbohydrate-hydrolyzing enzymes a-glucosidase and a-amylase; and, eventually, to identify and quantify its bioactive compound(s). The S. malaccense leaf extract was a far better scavenger of DPPH and ABTS than of nitric oxide. It also inhibited a-glucosidase more significantly than the positive control, acarbose, but was a poor a-amylase inhibitor. Myricitrin was identified by using high-performance liquid chromatography (HPLC) and liquid chromatography-mass spectrometry (LCMS) techniques as the major bioactive compound present in the extract. The percent yield of myricetin derivatives in the extract was determined to be 3.3 ? 0.05 . The presence of the potent antioxidant and antihyperglycemic agent myricitrin in the S. malaccense leaf extract indicates the potential use of the extract in the management of diabetes mellitus and its related complications.