We report a method for the synthesis of carbon nanotubes (CNTs) by microwave irradiation. CNTs were successfully synthesized by microwave heating of the catalyst loaded on various supports such as carbon black, silica powder, or organic polymer substrates (Teflon and polycarbonate). Microwave (2.45 GHz, 800 W) irradiation used acetylene as a hydrocarbon source, and 3d transition metals and metal sulfides were used as the catalysts. Different carbon yields and morphologies were obtained depending on the reaction conditions. Fibrous nanocarbons-linear or Y-branched-were observed as well as carbon nanoparticles and amorphous carbon. High-resolution transmission electron microscopy (HRTEM) revealed that these fibrous nano-carbons are either multiwalled CNTs or graphitic nanofibers (GNFs). This novel method has the potential to grow CNTs; virtually on any substrate provided its absorption of microwave energy is small.