Hybrid carbon nanofibers containing multiwalled carbon nanotubes (CNTs) were produced by electrospinning CNTs suspended in a solution of polyacrylonitrile in N,N-dimethylformamide, followed by carbonization and activation using a hydroperoxide-water steam mixture at 650 degrees C. Transmission electron microscopy and scanning electron microscopy were used to observe the morphology of the CNT-embedded carbon nanofibers. The specific surface area of the nanofibers was measured using the Brunauer-Emmett-Teller method. The electrochemical properties of the nanofibers were characterized by cyclic voltammetry and galvanotactic charge/discharge in 1MH(2)SO(4) electrolyte. The specific capacitance of electric double-layer capacitors containing CNT-embedded carbon nanofibers as electrodes reached 310 F g(-1), which is almost double that obtained for capacitors containing virgin carbon nanofibers as electrodes. The CNTs embedded in the carbonized electrospun nanofibers provide improved conductive pathways for charge transfer in the electrodes and therefore lead to a significantly enhanced specific capacitance.