In the three-phase liquid-membrane system consisting of water-nitrobenzene-water, the decrease in pH of aqueous phases is found to be accompanied with the spontaneous electric oscillation of several modes. The increase rates of proton concentration in each aqueous phase are found to differ considerably in each modes of electric oscillation. Furthermore, the presence of an aqueous phase without surfactant is found to accelerate the proton penetration rate through nitrobenzene-water interface. The mechanisms for each mode of oscillation are discussed.