In this work, we describe our efforts to produce Mn3O4–graphene nanocomposites based on a convenient andfeasible solution based synthetic route under mild conditions. According to transmission electron microscopy (TEM) and high angle annular dark field scanning transmission electron microscopy (HAADF-STEM) results porous Mn3O4 nanocrystals (NCs), 20–40 nm in size, are uniformly deposited on both sides of the graphene nanosheet (GNS) matrix. Significantly, the as-prepared Mn3O4–graphene nanocomposites exhibit remarkable pseudocapacitive activity including high specific capacitance (236.7 F g–1 at 1 A g–1), good rate capability (133 F g–1 at 8 A g–1), and excellent cyclability (the specific capacitance only decreases by 6.32 % of the initial capacitance after 1000 cycles). The excellent pseudocapacitive performance of the Mn3O4–graphene nanocomposites electrode is probably due to the positive synergistic effects between the Mn3O4 and GNS. Namely, the intimate combination of the conductive graphene network with uniformly dispersed porous Mn3O4 NCs not only greatly improves the electrochemical utilization of Mn3O4, but also increases the double-layer capacitance of the graphene sheets. These characteristics make this nanocomposite a very promising electrode material for high performance supercapacitors.