Toward the fast development of portable devices, the lightweight, flexible, and even wearable energy storage devices are very required. One effective device is the graphene-based fiber supercapacitors. Here we present the core-shell Co3O4/graphene hybrid fibers by hydrothermal method for the first time, where Co3O4 directly grows on the surface of graphene forming excellent hierarchical nanostructures. The combination of the Co3O4 shell and graphene core evidently improves the capacitive behaviors of the hybrid fibers. The Co3O4/graphene hybrid fibers are lightweight, flexible, and wearable, showing ultrahigh electrochemical performances such as large specific capacitance of 236.8 F g(-1) (196.3 mF cm(-2)) at current density of 0.2 A g(-1), outstanding rate capability, and excellent cycling stability (72.7% retention after 10000 cycles). The high electrochemical performances reveal the great potential of core-shell Co3O4/graphene hybrid fibers as electrodes in the energy storage system.