Metal oxide derived from metal-organic framework (MOF) could possess unique architecture and special properties. In this work, hierarchically nanostructured Mn₃O₄ is synthesized from the thermal annealing of manganese-1,3,5-benzenetricarboxylate (Mn-BTC) MOF with the presence of reduced graphene oxide (rGO) to yield rGO/Mn₃O₄ composite for the high-performance supercapacitor electrode material. The porous rGO aerogel is prepared from the hydrothermal and freeze-drying processes. The effective combination of Mn-BTC and rGO aerogel is realized through a facile ball-milling method that endows Mn-BTC with a rod-like structure in the composite. Upon annealing, the Mn-BTC-derived Mn₃O₄ presents the unique structure of porous rods comprising nanoparticles in the resulting rGO/Mn₃O₄ composite. The optimized rGO/Mn₃O₄/Ni foam electrode achieves a specific capacitance of 420 F g^-1 at 0.5 A g^-1 and a superior cycling property. The assembled all-solid-state symmetric supercapacitor based on rGO/Mn₃O₄ composite delivers the energy density of 22.1 Wh kg^-1 and power density of 3.0 kW kg^-1. The excellent capacitive performance of the rGO/Mn₃O₄ electrode could be ascribed to the effective integration of Mn-BTC-derived manganese oxides with hierarchical structure and the rGO matrix, facilitating the ion/electron transport in the electrochemical process.