Poly(vinyl alcohol)-niobium oxide (Nb2O5) composite nanofibers (precursors) were formed by electrospinning employing water as a solvent for the spinning solution. The precursors were converted into Nb2O5 or carbide (NbC) nanofibers by heating them in air or Ar. Hexagonal Nb2O5 nanofibers with high-specific surface area were obtained by heat-treatment of the precursors in air. NbC nanofibers could be obtained below theoretical temperatures calculated from thermodynamics data, indicating that the precursor is a nano-scale mixture of Nb and carbon sources.