A highly flexible Mn3O4/reduced graphene oxide (rGO) nanohybrid paper with high electrical conductivity and high mass loading of Mn3O4 nanofibers (0.71 g cm(-3)) is developed via a facile gel formation and electrochemical reduction process, which is low-cost, environmental friendly, and easy to scale up. Confined Mn3O4 nanofibers are well dispersed within the rGO sheets, which demonstrate to be a promising cathode material for flexible asymmetric supercapacitors (ASCs). When coupled with an electrochemically reduced rGO paper as the anode, a flexible ASC device, based on the Mn3O4/rGO nanohybrid paper as the cathode, is assembled; and it demonstrates remarkable electrochemical performance: a high volumetric capacitance of 54.6 F cm(-3) (546.05 mF cm(-2)), and remarkable volumetric energy and power density (0.0055 Wh cm(-3) and 10.95 W cm(-3)) being achieved with excellent cycling ability. The nanohybrid paper shows great improvement for flexible energy devices in terms of electrochemical properties.