A method of producing a carbon nanotube-containing composition is a method of producing a carbon nanotube-containing composition for synthesizing carbon nanotube aggregates by introducing a ferrocene derivative, a sulfur compound, a carbon source, and a carrier gas into a gas phase flowing in a heating furnace within a temperature range of higher than 1,200° C. to 1,800° C. The carbon source substantially consists of benzene or toluene. The carrier gas includes hydrogen at 10% by volume to 85% by volume. The carrier gas has a linear velocity of 500 cm/min to 2,200 cm/min.