Copper nanoparticles (Cu-NPs) have been electrochemically synthesized onto a poly(o -phenylenediamine) (PoPD-) coated glassy carbon electrode (GCE). Electrochemical properties and surface characterizations were studied using cyclic voltammetry, atomic force microscopy (AFM), scanning electron microscopy (SEM), and X-ray diffraction (XRD) analysis. Cyclic voltammetry, AFM, SEM, and XRD confirmed the presence of Cu-NPs on the electrode surface. Cu-NPs are firmly stabilized by surface attachment of the PoPD functionality that can be attached to the electrode surface, thus becoming an integral part of the polymer backbone. The Cu-NPs–polymer film-coated GCE (Cu-NPs/PoPD/GCE) showed excellent electrocatalytic activity toward the reduction of hydrogen peroxide (H2O2) and nitrite (NO−2) . Amperometry was carried out to determine the concentration of H2O2 and NO−2 at −0.3 V. The dependence of the current response on the H2O2 concentration was explored under neutral conditions, and an excellent linear concentration range from 1.0×10−6 to 1.0×10−3M was found. The Cu-NPs/PoPD/GCE allows highly sensitive, low working potential, stable, and fast amperometric sensing of H2O2 and NO−2 . This is promising for the future development of nonenzymatic sensors. The real-sample analysis of commercial H2O2 samples was performed using the proposed method, and the obtained results are satisfactory.