A method for fabricating a plurality of carbon nanotube structures having enhanced length is disclosed. Several steps are involved in this method. First, a substrate is provided. Next, a non-catalytic metal layer is formed on the substrate. Then, a catalytic metal layer is formed on the non-catalytic metal layer. After that, the catalytic metal layer is subjected to ultrasonication and exposure to water. Finally, the plurality of carbon nanotube structures is formed on the substrate in the presence of the catalytic metal layer. In this embodiment, the ultrasonication and exposure to water step includes submerging the catalytic metal layer in a liquid bath, ultrasonicating the catalytic metal layer and the liquid bath, and exposing the catalytic metal layer to water.