A method for manufacturing open-ended carbon nanotubes is described. The method includes steps of: providing a substrate having a catalyst layer formed thereon; placing the substrate in a reaction chamber; introducing a carbon source gas containing carbon element into the reaction chamber for growing carbon nanotubes form the catalyst layer; promptly reducing a concentration of the carbon source gas when the growth of carbon nanotubes in process, thereby ceasing the growth of the carbon nanotubes instantly; and separating the carbon nanotubes from the catalyst layer.