Mesoporous Nb₂O₅ nanofibers were scalable fabricated via a typical electrospinning method and a specific vapor hydrolysis, followed by an annealing treatment. The uniformly distributed mesopores of ~10 nm are generated through the controllable vapor-phase hydrolysis process without any addition of either hard template or surfactant, which is proved to be a contamination-free and environment-friendly method to obtain mesoporous Nb₂O₅. According to the merits of layered structure of orthorhombic Nb₂O₅ (T-Nb₂O₅) and large scale of mesopores for fast Li and Na ions transportation, the resulting Nb₂O₅ nanofibers exhibit outstanding electrochemical performance for both lithium and sodium storage, especially show an excellent capacitor-like high-rate performance. In order to explore the origin of these ultrafast charge storage properties, the charge storage kinetics was investigated by cyclic voltammetry. The analytic results reveal a surface-controlled kinetics, which is characteristic of capacitive behavior. Due to the pseudocapacitive charge storage properties, mesoporous Nb₂O₅ fibers display both high energy density and power density. The facile fabrication of high quality mesoporous Nb₂O₅ nanofibers and the demonstration of good pseudocapacitive behavior show the great potential of mesoporous Nb₂O₅ for applications in fast energy storage fields.