One-dimensional nanostructures comprising MoSe2 nanosheets and carbon with uniformly distributed nanovoids are prepared through the application of a simple selenization treatment to electrospun nanofibers. Size-controlled polystyrene nanobeads in the form of an aqueous suspension are introduced for the first time as an electrospinning solution, which enables the precise control of void size and uniform distribution of nanovoids in the one-dimensional (1D) nanostructure. The discharge capacity and Coulombic efficiency of the porous MoSe2/C composite nanofibers after the 200th cycle at a current density of 0.2 A g(-1) are 454 mA h g(-1) and 98.4%, implying efficient Na+ ion insertion and extraction in the composites. In addition, a high discharge capacity of 280 mA h g(-1) at a current density of 7.0 A g(-1) demonstrates an excellent rate capability and fast Na+ ion and electron transfer. Few-layered MoSe2 and highly conducive carbon facilitate ion and electron diffusion during cycling. Uniformly distributed nanovoids in the structure can accommodate the volume expansion induced by electrochemical reaction of Na+ ions with the composites and allow efficient penetration of electrolyte into electrodes.