A method of massively synthesizing double-walled carbon nanotubes is provided. In the method, catalyst metal particles having a size of a few nanometers are embedded in nano pores of a support material powder. Then, the support material powder embedding the catalyst metal particles is sintered at a temperature of 700-900.degree. C. Then, the support material powder embedding the catalyst metal particles is loaded in a reactor. Thereafter, high purity double-walled carbon nanotubes are formed massively by vaporizing a carbon source solution at a temperature of 700-1100.degree. C. and supplying the vaporized carbon source gas, or by directly supplying a carbon source gas to the reactor.