Diospyros dumetorum is an important folk medicine for treating pulmonary abscess and inflammation. The leaves of D. dumetorum revealed xanthine oxidase (XOD) inhibitory activity. With the guidance of UFLC-MS-IT-TOF analyses combined with bioassay in vitro, 15 flavonoids were isolated from the active parts of D. dumetorum. Except for 11 (IC50> 200 mu M), all compounds showed obvious XOD inhibitory activity with IC50 values of 32.5 +/- 0.7 similar to 145.0 +/- 3.3 mu M. The preliminary structure-activity relationships study suggested that glycosylation on C-3 was unfavorable for XOD inhibitory activity; hydroxyl groups on ring B were essential for maintaining activity; the activity was closely related with the position of galloylation. This is the first recognition of the XOD inhibitory activity and active constituents of D. dumetorum, and will provide valuable information for this plant as a new resource for treating hyperuricemia and gout.