The effect of 4-chlorophenol （4-CP） on the electrochemical activity of Ti-based IrO2 electrodes in acidic aqueous solutions was investigated within the electrochemical window for 4-CP. Cyclic voltammetry （CV） and electrochemical impedance spectroscopy （EIS） measurements both indicated that the existence of 4-CP in solution resulted in the activation of the IrO2 electrode in the electrochemical window. However, the testing results at metallic Ir electrode showed that the electrode activity was inhibited by 4-CP because of its adsorption onto the metal surface. A possible mechanism is proposed based on the influence of 4-CP on the electrochemical activities of these two electrode materials. The activation of IrO2 is believed to be related to its ease of transition from lower-valent to higher-valent oxides in the electrochemical window. The later oxides can be chemically oxidized and can remove organic molecules that are adsorbed onto the oxide electrode surface.