Mesoporous nanocomposite of polythiophene and MnO2 has been synthesized by a modified interfacial method, aiming to develop electrode materials for supercapactitors with an enhanced cycle performance and high-rate capability. The N2 adsorption/desorption isotherm test of the prepared hybrid indicates a high surface area and a typical mesoporous feature. A uniform hierarchical microstructure with submicron-spheres assembled from ultrathin nanosheet with diameters less than 10nm has been confirmed by field-emission scanning electron microscopy and transmission electron microscopy. The employed interfacial synthesis is found to be advantageous to retard the overgrowth of nuclei. The retention of 97.3% of its initial capacitance after 1000 cycles at a charge/discharge rate of 2Ag−1 indicates excellent cycle performance of the nanocomposite electrode. At a high-rate charge/discharge process of 10Ag−1, the nanocomposite electrode retained 76.6% of its capacitance at 1Ag−1, suggesting good high-power capability. The important roles of polythiophene in the as-prepared nanocomposite are highlighted in terms of their functions on enhancing the electrical conductivity and constraining the dissolution of manganese oxides during charge–discharge cycles.