Abstract: Electrochemically fabricated prussian blue (PB) film modified platinum electrode was studied by cyclic voltammetric and electrochemical impedance techniques. The redox process of the modified layer was discussed with the observed CV plot. The measured impedance spectrum was analyzed and the corresponding equivalent circuit was proposed. The apparent chargetransfer rate constant and the apparent diffusion coefficient of PB redox couple within the modified layer were obtained. The dependence of impedance behaviors of the PB films on varied film thickness was systematically studied. When the modified layer was relatively thin, the apparent chargetransfer rate constant and apparent diffusion coefficient increased with the increasing thickness of PB film and the charge transfer process was enhanced obviously. The charge transfer process was predicted to be controlled by the kinetic factors. On the other hand, if the modified PB layer was comparatively thicker, the charge diffused with restricted rate, and would only reach to a certain distance inside the modified film. The results were well satisfied with the multilayer model of spaced distributed redox modified electrode found in literature.