A glassy carbon electrode (GCE) is modified with electropolymerized film of p-aminobenzene sulfonic acid (p-ABSA) in pH 7.0 phosphate buffer solution (PBS). A poly(p-ABSA) modified glassy carbon electrode was used for the voltammetric determination of oxcarbazepine. The modified electrode exhibited excellent electrocatalytic activity for the reduction of oxcarbazepine. The voltammetric response of oxcarbazepine at this polymer film modified electrode increased significantly when compared with that at a bare glassy carbon electrode. The proposed method was applied to the quantification of oxcarbazepine in pharmaceutical formulations. The proposed method exhibits good recovery and reproducibility. The mechanisms of electropolymerization of p-ABSA and reduction of oxcarbazepine are also suggested.