Provided is a method for producing a carbon nanotube, wherein a catalyst for carbon nanotube production comprising a powdery catalyst supporting a metal on magnesia and having a bulk density of 0.30 g/mL to 0.70 g/mL, in a vertical reactor, is disposed over the whole area in a horizontal cross section direction of the reactor, in such state a carbon-containing compound flowed in a vertical direction inside the reactor is contacted with the catalyst at 500 to 1200.degree. C., thereby carbon nanotubes of uniformity and high quality are efficiently synthesized in a large amount.