The equilibrium free energy of activation for electron-transfer processes across liquid/liquid interfaces is estimated using the desolvation energies, interfacial solvation numbers, and inner potential difference between the bulk and the interface for the ionic species and dielectric permittivities. The analysis employing a sharp boundary model is shown to yield a quantitative expression pertaining to the free energy of activation, solvent reorganization energy, and the rate constant. The methodology is applied to the electron transfer of [Fe(CN)(6)](3-)/[Fe(CN)(6)](4-) with (i) [Lu(biphthalocyanine)](4+)/[Lu(biphthalocyanine)](3+) and (ii) TCNQ/TCNQ(-)redox couples in water/1,2 dichloroethane interface.