Cedrela sinensis leaf is used as a seasonal vegetable in Korea. The 70% ethanol extract of these leaves exhibited potent xanthine oxidase (XO) inhibition. To investigated the compounds responsible for this effect, bioassay-guided purification of the butanol fraction led to the isolation of 5 metabolites which were identified as rutin (1), isoquercitrin (2), pentagalloyl glucose (3), quercetrin (4), and afzelin (5) by detailed spectroscopic analyses, including UV, MS, and 2D NMR techniques. Importantly, compound 3 was not only the most potent component with IC50 = 2.8 µM, but also similar inhibitory activity to the allopurinol (IC50 = 2.3 µM) used as XO inhibitor for clinical management of Gout. In kinetic mechanism study, XO inhibitor 3 was reversible noncompetitive-type inhibition characteristics. Furthermore, the most potent XO inhibitor 3 was proven to be present in high quantities in the leaves by a UPLC-qTof MS analysis. This result contributes to our understanding of C. sinensis leaves utility as functional food stuff and widely used herbal medicine.