We report the electropolymerization of K2PtCl6 on various electrode substrates by the cyclic scanning of the potential in the presence of CuCl2 and in the potential range between 700 and -800 mV (vs. SCE). Cu2+ was found to be a necessary ion for the formation and stabilization of the polymeric film. The potential range of the cyclic scanning was found to be crucial for the formation of the : film. An energy dispersive X-ray spectrometry study of the modifier film indicates that it contains copper, platinum, and chloride ions, respectively. The scanning electron microscopy image reveals the formation of the nanometer-sized modifier particles dispersed on the substrate electrode. The electrochemical behavior of the modified electrode was studied in detail in electrolyte solutions containing various cations including Cu2+, H+, Fe3+, Cr3+. On the basis of these studies, a mechanism of the electropolymerization on the substrate surface was proposed which suggests for the modifier film a one-dimensional, polymeric, mixed-valent, and negative-charge-carrying platinum complex stabilized by the Cu2+/Cu+ as the counter ions. The composition of the modifier film is therefore proposed to be [CuPtCl6 . CuPtCl4](n), and denoted as CuPtCl6\GC to signify the necessary starting components. H+/H, Fe3+/Fe2+ and Cr3+/Cr2+ display remarkably reversible redox behavior at the CuPtCl6\GC electrode. The modified electrode also displays very good electrocatalytic activity in the oxidation of ascorbic acid, H2O2, S2O32-, and NO.