The present invention is to provide a process for the preparation of carbon nanotubes or nanofibers, which comprises introducing in a gaseous phase a colloidal solution of metal nanoparticles optionally containing a surfactant together with an optional carbon source into a heated reactor, and carbon nanotubes or nanofibers thus prepared.According to the present invention, the shape and structure of carbon nanotubes or nanofibers can be easily controlled, the carbon nanotubes or nanofibers can be continuously produced in large scales, the apparatus and the process for the preparation of nanotubes or nanofibers are simplified, and carbon nanotubes or nanofibers having various shapes, structures and properties can be easily and cheaply prepared. Further, the process of the present invention is highly reproducible and favorable in industry.