Abstract: Objective:The best conditions of synthesizing quercetin isopentenyl modifier and the antioxidant activity of modified products were discovered. Methods:The Williamson forming ether method was adopted to synthesizing quercetin isopentenyl modifier with quercetin and prenyl bromide as raw reactants. Moreover, the scavenging effects of modified products in vitro on superoxide anion (by pyrogallol autoxidation method) , DPPH radical and hydroxyl radicals (by Fenton reaction method) were evaluated. Results:The optimal reaction conditions to synthesize quercetin modifier were quercetin and prenyl bromide ratio of 1∶1, the catalyst role of anhydrous potassium carbonate, 60℃ water bath reflux condensation reaction 8h, separated by column chromatography to obtain modifications. HPLC retention times of the product detected later than quercetin, the product obtained may have two, peak area 48.9%. Quercetin by isopentenyl modification, the resulting products on hydroxyl radical and superoxide anion scavenging rate was significantly increased, but the removal of the DPPH radical was lower than that of quercetin. Conclusion:After quercetin was modified by isopentenyl, the resulting product was a new active compounds which have higher biological activity than quercetin.