A cyclic voltammetric method is presented for the determination of antioxidant activity of flavonoids in the presence of DPPH center dot as target radical. The method depends on the scavenging effect of the radical as monitored by the decrease in peak currents accompanying an increase in the concentration of flavonoids. For this purpose the electrochemical behavior of DPPH was investigated in DMSO at 25 +/- 0.5 degrees C. The antioxidant activity coefficient, (K-ao), was estimated from the linear part of a plot of the change in current density vs flavonoid concentration. The antioxidant capacity index (IC50, corresponding to 50% consumption of DPPH center dot) was also calculated from the proportional current decrease for a relative comparison among the flavonoids. Mechanism of the electrochemical process is explicated and it is proposed that hydrogen atom transfer (HAT) from the flavonoid to DPPH center dot is responsible for the antiradical activity. The proposed electrochemical analysis is validated by the well established UV-Visible spectroscopic method. (C) 2012 The Electrochemical Society. [DOI: 10.1149/2.jes112300] All rights reserved.