Abstract This work demonstrated a novel and simple route for preparing a composite comprising of manganese oxide (MnO 2) nanoparticles and polyaniline (PANI) doped poly(4-styrene sulfonic acid-co-maleic acid) (PSSMA) by “electrochemical doping-deposition”. The PANI–PSSMA–MnO 2 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 MnO 2 nanoparticles in the porous structure of PANI–PSSMA structure. XRD measurements showed the distortion of the crystal structure of β-MnO 2 after deposition of MnO 2 in PANI–PSSMA structure. Thus, the XRD pattern of PANI was predominating. Cyclic voltammetry and chronopotentiometry were employed in 0.5 M Na 2SO 4 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–MnO 2 (50.4 F g −1) had improvement values of 172% compared to that of PANI (18.5 F g −1). When only the MnO 2 mass was considered, the composite had a specific capacitance of 556 F g −1.