Electrical potential oscillation across a liquid membrane of a water/octanol/water system, in which a surfactant and ethanol are present in one of the waters, and electrical potential between octanol and aqueous phases of the octanol/water system were measured. On using sodium dodecyl sulfate (SDS) as the surfactant, potential oscillation was initiated with a sudden potential change toward the more negative potential, The upper potential (E(A,SDS)) and lower potential (E(B,SDS)) of the first oscillation were affected by the electrolyte added to the aqueous phase containing no previous surfactant. With hexadecyltrimethylammonium bromide (CTAB) as the surfactant, direction of the pulse was opposite that when using SDS. The lower potential (E(A,CTAB)) and upper potential (E(B,CTAB)) of the first oscillation were affected by the electrolyte. For instance, E(A,SDS) and E(B,CTAB) were greatly affected by halide ion size. In contrast, E(A,CTAB) and E(B,SDS) were only slightly affected by this parameter. The effects of the electrolytes on E(A,SDS) and E(B,SDS) were essentially the same as those on potentials at the interface between the octanol and aqueous phases of the octanol/water system in the absence of SDS (E(C,SDS)) and presence of SDS (E(D,SDS)), respectively. The effects of electrolytes on E(A,CTAB) and E(B,CTAB) were also basically the same as those on the potentials at the interface between the octanol and aqueous phases of the octanol/water system in the absence of CTAB (E(C,CTAB)) and presence of CTAB (E(D,CTAB)), respectively. Potential oscillation thus appears quite likely due to the repetitive formation and destruction of the surfactant layer adsorbed on the octanol/water interface.