Polyaniline/mesoporous carbon/MnO2 (PANI/CMK-3/MnO2) ternary nanocomposites with a PANI nanolayer uniformly deposited on the CMK-3/MnO2 particles were synthesized by chemical oxidative polymerization. Structure and morphology of the ternary composites were further characterized by TEM, XRD, FTIR and FE-SEM techniques. Electrochemical measurements demonstrated that the ternary composite with 12% MnO2 content possessed enhanced specific capacitance of 695Fg−1 and the capacitance retention was 88% after 1000 galvanostatic charge-discharge cycles at a current density of 1.0Ag−1. The incorporation of MnO2 nanoparticles can not only contribute to high capacitance but also stabilize the interaction between the quinoid ring of PANI and the CMK-3/MnO2 particles. The PANI nanolayer in the ternary composite restrains the dissolution of MnO2 nanoparticles in acidic electrolyte so as to enhance their electrochemical utilization. The synergistic effect among three components may result in enhanced specific capacitance and cycling stability of the ternary composites.