Fiber electronic devices show advantages for the direct use as wearable and embedded device units or integrated textile modules. We successfully developed a coaxial-type flexible fiber supercapacitor by using NiCo2O4 nanosheets grown on Ni wire as the fiber electrodes. The volume capacitance of the fiber-shaped supercapacitor reached 10.3F/cm3 at a current of 0.08mA and outstanding cycling stability. An energy density of 1.44mWhcm−3 and a power density of up to 17Wcm−3 were also obtained for the fiber supercapacitor, which are almost 48-fold higher than the previous values. Furthermore, the coaxial-type fiber supercapacitor does not show any apparent degradation in the bending test, illustrating the promise for use as electrodes for portable and wearable energy storage.