The present invention provides a nanostructure made of V group transition metal dichalcogenide such as NbSe2 and a method for preparing such a nanostructure. A nanofiber and nanotube comprising crystals of V group transition metal dichalcogenide such as NbSe2 or TaS2 have electric properties identical to those of a bulk single crystal. The preparation method is as follows: high-purity Nb and Se which are starting materials and which are mixed in a stoichiometric ratio are allowed to react with each other at 800° C. or less in a vacuum with a temperature gradient of 1 k/cm. In a method for preparing nanofibers or nanotubes from NbSe2 that is a starting material by a chemical transport process using a iodine acting as a medium, if C60 acting as a promoter is used, nuclei for forming the nanofibers or the nanotubes can be efficiently produced. Initial nanoparticles surrounding a C60 molecule form nanorings, which grow into the nanotubes. Other nanoparticles surrounding no C60 molecule grow into the nanofibers. The nanofibers prepared as described above have a diameter of 150 nm and a length of 10 μm.