High-porosity MnO2 with a mesoporous structure is synthesized through a facile redox reaction, and the polypyrrole (PPy) nanofilms are grown on the synthesized mesoporous MnO2 by chemical vapor deposition to form a 3D nanocomposite structure. The as-prepared high-porosity MnO2/PPy with a nanocomposite structure presents a high specific capacitance of 320 F g(-1) and a 91.4% capacitance retention after 5000 charge-discharge cycles. MnO2/PPy and N-doped active carbon are employed as a positive electrode and a negative electrode, respectively, to assemble an asymmetric supercapacitor (ASC), which exhibits a high energy density of 38.6 Wh kg(-1) at 0.5 A g(-1) and long-term cyclic stability (90.6% capacity retention after 5000 cycles). Such high-performance capacitive behavior is attributed to the high porosity, mesoporous structure, and improved electrical conductivity of the fabricated ASC, which is promising for various supercapacitor applications. (C) 2016 Elsevier B.V. All rights reserved.