Fiber-based supercapacitors (FSCs) are new members of the energy storage family. They present excellent flexibility and have promising applications in lightweight, flexible, and wearable devices. One of the existing challenges of FSCs is enhancing their energy density while retaining the flexibility. We developed a facile and cost-effective method to fabricate a highly capacitive positive electrode based on hierarchical ferric-cobalt-nickel ternary oxide nanowire arrays/graphene fibers and a negative electrode based on polyaniline-derived carbon nanorods/graphene fibers. The elegant microstructures and excellent electrochemical performances of both electrodes enabled us to construct a highperformance flexible asymmetric graphene fiber-based supercapacitor device with an operating voltage of 1.4 V, a specific capacitance up to 61.58 mF·cm^–2, and an energy density reaching 16.76 μW·h·cm^–2. Moreover, the optimal device presents an outstanding cycling stability with 87.5% initial capacitance retention after 8, 000 cycles, and an excellent flexibility with a capacitance retention of 90.9% after 4, 000 cycles of repetitive bending.