Various SWNT samples as either catalyst or catalytic support were used in the chemical vapor deposition (CVD) method for the growth of MWNTs. Catalysts were prepared by the impregnation of SWNT soot with different transition metals. Decomposition of acetylene was investigated at different temperatures (650–720 °C). The quality of both original SWNTs and the newly formed carbon nanostructures was assessed by TEM. A significant difference was found between selectivities of original (known as metallic impurities in SWNT soot) and the posteriorly deposited metallic particles. In the presence of active catalyst SWNT ropes tend to disappear, absorbed into carbon fibers or MWNTs.