Poly(o-phenylenediamine) films were electrochemically prepared on gold electrodes from the corresponding monomer in an aqueous solution at a constant potential. The polymeric films prepared in this one-step procedure were found to be thin and insoluble in the aqueous solution. Cyclic and differential pulse voltammetric techniques were used to examine the permeation properties of ascorbic acid and dopamine at the resultant polymeric film electrode. Then, the effects of the chemical and electrochemical variables (e.g., film thickness, polymerization potential, concentrations of monomer and electrolyte) on the permselectivity characteristics of the polymeric film were systematically investigated and the optimal values for each parameter were determined. Furthermore, it was found that the optimized polymer electrode was found to be stable for the successive runs. As a result, it is claimed that poly(o-phenylenediamine) film can be used as a dopamine-selective polymeric membrane.