Abstract: The anodic reaction of oxygen evolution on PbO₂ electrode was studied by A. C. impedance measurement. The Faradaic. resistance R_t,double layer capacitance C_d adsorption resistance R_a and adsorption capacitance C_a were determined by analyzing the impedance spectra with microcomputer curve-fitting method. The rate-controlling step of the reaction was considered to be (OH)_ad+H₂O→(O)_ad+H₃O+e^-. The relation between C_d, C_a.and OH^-ion concentration was discussed in view of the adsorption effect.