Abstract: The deactivated MMO oxides used in seawater electrolysis in nuclear power plant and the fresh oxides were compared.Their morphologies、compositions and phase structures were determined by means of scanning electron microscope,energy dispersive X-ray detector and X-ray diffraction.The electrochemical properties of the anodes were characterized by accelerated life test,cyclic voltammetry and electrochemical impedance spectrum.The results showed that solid solution structures(Ru,Ir,Ti)O₂ and(Ir,Ti)O₂ formed after pyrolysis,the solid solution structures and active components disappeared after the deactivation of the anodes.Electrochemical test results indicated that the active area decreased and the coating resistance increased,which was caused by active component falling off from anode surfaces.It can be concluded that the deactivation of the oxide anodes was resulted from the detachment of active component.