A promising energy storage material, MnO2/hierarchically porous carbon (HPC) nanocomposites, with exceptional electrochemical performance and ultrahigh energy density was developed for asymmetric supercapacitor applications. The microstructures of MnO2/HPC nanocomposites were characterized by transmission electron microscopy, scanning transmission electron microscopy, and electron dispersive X-ray elemental mapping analysis. The 3–5 nm MnO2 nanocrystals at mass loadings of 7.3–10.8 wt % are homogeneously distributed onto the HPCs, and the utilization efficiency of MnO2 on specific capacitance can be enhanced to 94–96 %. By combining the ultrahigh utilization efficiency of MnO2 and the conductive and ion-transport advantages of HPCs, MnO2/HPC electrodes can achieve higher specific capacitance values (196 F g−1) than those of pure carbon electrodes (60.8 F g−1), and maintain their superior rate capability in neutral electrolyte solutions. The asymmetric supercapacitor consisting of a MnO2/HPC cathode and a HPC anode shows an excellent performance with energy and power densities of 15.3 Wh kg−1 and 19.8 kW kg−1, respectively, at a cell voltage of 2 V. Results obtained herein demonstrate the excellence of MnO2/HPC nanocomposites as energy storage material and open an avenue to fabricate the next generation supercapacitors with both high power and energy densities.