Double layer effects on the kinetics of the Cs+ ion transfer across the water/nitrobenzene interface were studied by an ac polarographic technique. Apparent kinetic parameters agree well with those reported previously. By applying the Frumkin-type correction based on the Gouy-Chapman theory, the non-linear Tafel plots were inferred indicating some dependence of the charge transfer coefficient on the interfacial potential difference. The latter effect can weaken the contribution of the diffuse-layer potentials to the apparent kinetic parameters, thereby accounting in part for the observed negligible change of these parameters with the aqueous electrolyte concentration. The Frumkin-type correction failure at low electrolyte concentrations and high surface charge densities is due to an overestimation of the diffuse/layer potential by the Gouy-Chapman theory, rather than due to the dynamic (Levich) effect of the diffuse double layer.