Electrochemical impedance spectroscopy (EIS) was used as the main technique coupled with cycling voltammetry (CV) to characterize the surface fouling of a conventional Ti/IrO2 in 4-CP aqueous solutions caused by the electropolymerization of chlorinated phenol. Capacitive information of polymeric films formed was successfully derived from both the on-line and off-line impedance measurements and was used to characterize the surface fouling of IrO2 electrodes. Results showed that the fouling extent at IrO2 electrode decreased when its heating temperature was increased. With increasing the anodic potential, the surface fouling was enhanced firstly and then weakened, reaching the highest extent at 0.9 V. More positive potentials were believed to further oxidize the formed films and thereby to reactivate the deactivated electrode surface. With the increase of positive potential, the regeneration was enhanced, but no entire recovering could be achieved after the reactivation even at very high potentials. (C) 2007 Elsevier Ltd. All rights reserved.