Abstract: The reactions between bromine and some flavonoids including daidzein, daidzin, puerarin, 7-hydroxyl-4'-methoxy isoflavone, 7-hydroxyl flavone, 5,7-dihydroxyl flavone, 7,4'-dihydroxyl flavone, apigenin, quercetin, hesperetin, luteolin, etc. were studied using coulometric method with electrolytically generated bromine. It was shown that the number of electrons involved depended on the molecular structure of the flavonoid and also on the titration conditions.The reaction product of daidzein was examined by mass spectrometry and the results clarified the reaction mechanism.This work is useful not only for the analysis of the flavonoids but also has some theoretical interest.