Electrochemical polymerization of benzene has been carried out in a one-compartment cell using indium-tin oxide conducting glass as a working electrode and Pt mesh as a counterelectrode by the use of a composite electrolyte of aluminum chloride and copper(I) chloride in nitrobenzene. On applying a constant voltage at + 1.8 V vs SCE, a brown and flexible polyparaphenylene (PPP) film was smoothly obtained on the ITO anode surface. The electrical conductivity of the film as grown was 1.9 × 10−5S/cm. Aluminum and chlorine atoms were detected in the film from XPS studies, so the film might contain AlCl4−(and Cl−) as a dopant. Scanning electron micrographs of the growing side surface of the film prepared at a constant potential of + 1.8 V vs SCE showed a fibrillar morphology. The fibril diameter (∼100 nm) was similar to that of a polyaniline film. The PPP film exhibited a spin concentration of 1.0 × 1019spins/g, which corresponds to 800 phenylene units per spin. The g-value and the peak-to-peak linewidth were 2.0045 and 7 G, respectively.