A method for manufacturing a carbon nanotube assembly including the steps of: forming metallic fine particles, having a predetermined particle diameter, on a substrate; heating the metallic fine particles to a predetermined temperature of 300.degree. C. to 400.degree. C. in a reducing atmosphere to cause reduction at surfaces thereof; heating the metallic fine particles to a predetermined reaction temperature in a reactor; and introducing an organic compound vapor into the reactor to grow carbon nanotubes on the metallic fine particles in such a way that a time during which the temperature of the metallic fine particles exceeds 450.degree. C. is 600 seconds or fewer for the period of time before the growth of the carbon nanotubes is started after the heating of the metallic fine particles is started.