The charge transfer mechanism at the water \ 1,2-dichloroethane (DCE) interface in solvent extraction of Ni(II) was investigated by electrochemical impedance spectroscopy (EIS) and spectrophotometry. The charge transfer species were identified by spectrophotometry using an optical fiber system. In the experimental I - E curves, the diffusion limiting current, which is related to the extraction rate, increases with increasing Ni(II) concentration in the aqueous phase and 8-hydroxyquinoline (HQ) concentration in the organic phase. The kinetic parameters were determined by numerical simulation for the experimental results of EIS. It was found that the solvent extraction rate was accelerated by the imposed potential and that the interfacial capacitance was a function of the amount of the intermediate.