Method for producing carbon nanotubes

A method for producing a mixture comprising carbon nanotubes and 0.1-0.5% by mass of silicon by fluidized chemical vapor deposition (CVD), the method comprising:

• heating an insertion material (A) in a reaction tube to 1200° C. or higher, wherein a sum of masses of Al2O3 and SiO2 in the insertion material (A) constitutes at least 90% of a total mass of the insertion material (A) and wherein a mass ratio of Al2O3/SiO2 in the insertion material (A) is in a range of 1.0 to 2.3;
• and
• bringing a gas present in an environment in which the material (A) is being heated to 1200° C. or higher, into contact with a feed gas to generate the mixture.