A simple electrochemical method for estimating the antioxidant activity (AA) of flavonoids has been developed. The proposed method is based on a measurement of the half-wave potential (E_1/2) of the first oxidation wave of flavonoids by using flow-through column electrolysis. At the same time, the lipid peroxidation (LPO) inhibiting effects of these flavonoids were determined. A quantitative structure-activity relationship was obtained to describe the AA of flavonoids: IC₅₀(μM) = 30.36 + 151.50E_1/2 (V) - 12.63log P (r = 0.852), where IC₅₀ represents the concentration for 50% inhibition of LPO, and P represents the octanol/water partition coefficient. This method is expected to be useful for the quick screening of flavonoid antioxidants, and evaluating the AA of flavonoid-containing foods and medicinal plants.