The transition metal-substituted Krebs-type polyoxometalates (POMs) [Sb2W20M2O70(H2O)(6)](n-), M = Fe(III), Co(II), or Cu(II), were surface immobilized within the conducting polymer 3,4-ethylenedioxythio-phene (PEDOT) on glassy carbon electrode surfaces. The immobilized films of different thicknesses were characterized by electrochemical and surface based techniques. The inherent redox activity for the Krebs-type POMs, [Sb2W20M2O70(H2O)](n-), M = Fe(III), Co(II), or Cu(II), that were observed in the solution phase were maintained in the polymeric PEDOT matrix. The resulting films were found to be extremely stable toward redox switching between the various POM-based redox states. The films exhibited pH-dependent redox activity and thin layer behavior up to 100 mV s(-1) The films were found to be highly conductive through the employment of electrochemical impedance spectroscopy. Surface characterization of the films was carried out by X-ray photoelectron spectroscopy, atomic force microscopy, and scanning electron microscopy graph.