Abstract:Objective: To study the inhibitory effect and mechanism of chemical constituents from Daphne giraldii on xanthine oxidase activity. Method: The ultraviolet spectrophotometry was adopted, xanthine as substrate and allopurinol as positive control drug, to measure xanthine oxidase activity affected by four compounds:luteolin(1), 5,7,3'-trihydroxy-4'-methoxy-flavone(2), daphnodorin A(3), daphnin(4) which were isolated from D. giraldii, and further the type of inhibition through enzyme kinetic was exploreds. Result: The compounds had obvious inhibiting effect on xanthine oxidase, among which 5,7,3'-trihydroxy-4'-methoxy-flavone(2)was a noncompetitive inhibitor while luteolin(1), daphnodorin A(3) daphnin(4)were competitive inhibitors. Conclusion: Flavonoids and coumarins in D. giraldii can effectively inhibit xanthine oxidase activity, which can provide theoretical basis for the clinical usage of D. giraldii in treatment of gout.