The mixed-signal Fourier-transform (FT) method for the electrochemical impedance spectroscopy (EIS) measurement has been developed to reduce both memory space and calculation time for computer-aided FT. In the conventional method, the FT is performed twice for the voltage and current signal. The proposed method combines the voltage and current signal, and the combined signal is Fourier transformed to obtain a spectrum function. The electrochemical impedance is extracted from the spectrum function. To validate the proposed method, EIS measurement for a polymer electrolyte membrane fuel cell was conducted with both the proposed method and a commercial impedance analyzer. The results obtained from these two methods agree in the magnitude and argument of the impedance.