p-Dimethoxybenzene is anodically oxidative polymerized to poly(2,5-dimethoxy-1,4-phenylene). p-Diethoxybenzene and p-dipropoxybenzene are also polymerized because the alkoxy groups reduce oxidation peak potentials of the benzene derivatives. This electro-oxidative polymerization is studied with the preparative electrolysis and cyclic voltammetry. The polymerization contains an electrophilic reaction of cation radical of the benzene and proceeds through a stepwise or chain propagation according to the supplied potential.