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A series of polysulfone membranes with different pore structures were prepared and characterized by electrochemical impedance spectroscopy (EIS). Two parameters, the membrane resistance and capacitance, were analyzed from the EIS data according to an equivalent circuit. It was found that the characteristic frequency obtained from the EIS data without any fitting was perfectly equivalent to the fitted parameters from theoretical calculations. Moreover, an additional time constant was observed under relatively low electrolyte concentration. This could be attributed to the capacitance response of the electrolyte at low electrolyte concentration and high frequency. The effect of electrolyte concentration on the impedance spectra of polysulfone membranes was then studied in detail, which can provide guidance for the selection of electrolyte concentration for efficient EIS analysis of membrane materials.