A facile electrospinning method with subsequent heat treatments is employed to prepare carbon nanofibers (CNFs) containing uniformly-dispersed Co3O4 nanoparticles as electrodes for supercapacitors. The Co3O4/CNF electrodes with about 68 wt.% active particles deliver a remarkable capacitance of 586 F g-1 at a current density of 1 A g-1. When the current density is increased to 50 A g-1, about 66 % of the original capacitance is retained. The electrodes also present excellent cyclic stability of 74% capacity retention after 2000 cycles at 2 A g-1. These superior electrochemical properties are attributed to the uniform dispersion of active particles in the CNF matrix which functions as a conductive support. The onion-like graphitic layers formed around the Co3O4 nanoparticles not only improve the electrical conductivity of the electrode, but also prevent the separation of the nanoparticles from the carbon matrix.