A novel structured porous nanofiber comprising MoSe2 nanosheets and carbon was 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. Few-layered MoSe2 and highly conductive 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. The simple synthetic method introduced in this study can be applied to the preparation of porous transition-metal compounds nanofibers with various compositions for a wide variety of applications, including energy storage.