We report the fabrication of sandwich-structured MnO2/graphene (MG) nanoflowers by an in situ chemical redox reaction between mesoporous carbon and KMnO4, which was characterized by various techniques. The results demonstrate that the mesoporous carbon was corroded into interconnected graphene framework with ultrathin MnO2 nanofilms deposited simultaneously on both sides of the as-generated graphene sheets. The as-synthesized MG exhibits excellent supercapacitive behaviours in a wide potential window from −0.2 to 1.2V vs. saturated calomel electrode with a 0.5M aqueous Li2SO4 solution as the electrolyte. Specially, the MG electrode delivers a reversible gravimetric capacitance of ∼240Fg−1 at 1Ag−1 for 1000 cycles with retention rate up to 96%. The significant synergistic efforts and structure hybridization contribute to such improved electrochemical properties, indicating that the MG hybrid holds great promise in the application of high-performance supercapacitors.