Layered graphene/manganese oxide (G/MnO2) nanocomposites for supercapacitor applications were prepared with a face-to-face electrostatic self-assembly method using high-quality graphene, which was obtained from the one-step electrochemical exfoliation of graphite. The results reveal that the graphene and MnO2 nanaosheets need to be oppositely charged for the electrostatic self-assembly process. The face-to-face contact between the MnO2 nanosheets and graphene can effectively improve the conductivity of MnO2 and prevent the restacking and agglomeration of graphene. In addition, the composites exhibit an electrochemical-activation behavior, and the ratio of MnO2/graphene in composites significantly influences the electrochemical performance. The G-2/MnO2 composite displays a specific capacitance of 319Fg−1 at 0.2Ag−1, and only 4.4% of the capacitance degrades after 10,000 cycles, which demonstrates the composite's excellent cycle stability. Furthermore, the composite features a high energy density of 31.5Whkg−1 at a power density of 100Wkg−1. This attractive performance makes it a promising candidate as an electrode material for supercapacitors. Remarkably, although the graphene content in G-4/MnO2 composite is the same, the specific capacitance reduced to 186Fg−1 due to the different mixing times.