This work demonstrated a novel and simple route for preparing a composite comprising of manganese oxide (MnO2) nanoparticles and polyaniline (PANI) doped poly(4-styrene sulfonic acid-co-maleic acid) (PSSMA) by “electrochemical doping-deposition”. The PANI–PSSMA–MnO2 composite was characterized by scanning electron microscopy (SEM)), X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS). SEM images revealed a uniform dispersion of MnO2 nanoparticles in the porous structure of PANI–PSSMA structure. XRD measurements showed the distortion of the crystal structure of β-MnO2 after deposition of MnO2 in PANI–PSSMA structure. Thus, the XRD pattern of PANI was predominating. Cyclic voltammetry and chronopotentiometry were employed in 0.5M Na2SO4 to evaluate the capacitor properties. The results showed a significant improvement in the specific capacitance of the composite electrode. The specific capacitance of PANI–PSSMA–MnO2 (50.4Fg−1) had improvement values of 172% compared to that of PANI (18.5Fg−1). When only the MnO2 mass was considered, the composite had a specific capacitance of 556Fg−1.