An ultrathin V2O5 layer was electrodeposited by cyclic voltammetry on a self-standing carbon-nanofiber paper, which was obtained by stabilization and heat-treatment of an electrospun polyacrylonitrile (PAN)-based nanofiber paper. A very-high capacitance of 1308 F g−1 was obtained in a 2 M KCl electrolyte when the contribution from the 3 nm thick vanadium oxide was considered alone, contributing to over 90% of the total capacitance (214 F g−1) despite the low weight percentage of the V2O5 (15 wt%). The high capacitance of the V2O5 is attributed to the large external surface area of the carbon nanofibers and the maximum number of active sites for the redox reaction of the ultrathin V2O5 layer. This ultrathin layer is almost completely accessible to the electrolyte and thus results in maximum utilization of the oxide (i.e., minimization of dead volume). This hypothesis was experimentally evaluated by testing V2O5 layers of different thicknesses.