We have investigated the formation of uniform and well-aligned multi-walled carbon nanotubes (MANTs) by controlling radio-frequency (rf) glow-discharge plasmas in weak and strong magnetic fields. The MWNTs growing directly on the rf electrode in the weak magnetic field (0.03 T) are deformed and combined with each other by the bombardment of the high energy ions generated by the large sheath electric field in front of the rf electrode. When the strong magnetic field (2 T) is applied, on the other hand, the MWNTs are observed to be well-aligned and not to be deformed. These results can be explained by the fact that the ion bombardment energy reduces in spite of the existence of the large sheath electric field, which is caused by the magnetization of the ions in the strong magnetic field. (c) 2005 Elsevier B.V. All rights reserved.