The preparation of composites of precise metal oxides/conducting polymers is important in studies of supercapacitors. In this work, a three-dimensional matrix of poly(3,4ethylenedioxythiophene)-poly(styrene sulfonic acid)-polyaniline (PEDOT-PSS-PANI) was prepared by interfacial polymerization of ANI into PEDOT-PSS. Conductivity was enhanced by incorporating of PANI into PEDOT-PSS because of the decrease in the distance for electron shuttling along the conjugated polymeric chain. Composite electrodes were prepared by the electrodeposition of manganese dioxide (MnO 2 ) in a PEDOT-PSS-PANI three-dimensional matrix. The electrodes were characterized by field emission scanning electron microscopy (FE-SEM), X-ray photoelectron spectroscopy (XPS), and cyclic voltammetry techniques. The results show a significant improvement in the specific capacitance of the composite electrode. For PEDOT-PSS the specific capacitance was of 0.23 F g -1 , while PEDOT-PSS-PANI and PEDOT-PSS-PANI-MnO 2 displayed values of 6.7 and 61.5 F g -1 , respectively. When only considering the MnO 2 mass, the composite had the specific capacitance of 372 F g -1 . The composite also had an excellent cyclic performance.