An electrochemical impedance spectroscopy (EIS) was applied to the investigation of the solvent extraction mechanism of metallic ions across a water/1,2-dichloroethane interface. In the electrochemical measurement, the transfer of a metallic ion-chelating reagent complex across the interface can be detected as the electrochemical response. Electrochemical impedance showed a capacitive semi-circle and an apparent Warburg impedance, indicating that the diffusion process contributed to the total transfer rate. A theoretical expression which represents the electrochemical impedance for solvent extraction of a metallic ion-chelating reagent complex was derived, and numerical simulations were performed. The rate constants obtained by the simulation were compared with the extraction constant.