In this paper, carbon nanotubes (CNTs) used as support and cobalt as catalyst to prepare new CNTs was studied. CNTs could grow well if the precursor CNTs were supported with Co on its surface. On the contrary, CNTs couldn’t grow at all if the precursor CNTs were not supported with Co. The TEM images showed that diameters of the obtained CNTs were different from those of the precursor CNTs. The pure CNTs could be prepared in this method without further purifying. The amount of Co on the precursor CNTs could affect the growth of CNTs greatly. When the content of metal on precursor CNTs was less than 16.2%, the amount of the obtained CNTs increased with the increasing amount of Co, and the maximum growth amount of 625% of CNTs could be obtained. But if the content of metal was more than 16.2%, the amount of Co had no influence on the growth of CNTs.
