Well-aligned carbon nanotubes were grown perpendicular to the surface of Ni substrates by hot-filament-assisted dc plasma chemical vapor deposition in a CH4/H-2 plasma. It was found, from observation by a scanning electron microscope and a transmission electron microscope, that the nanotubes starting from the side grew first parallel to the plasma boundary and then toward the plasma while those starting on the surface facing the plasma grew straight toward it. It has been suggested that force toward the plasma caused by the local electric field in the sheath and negative charge at the top of nanotubes assist them to grow well-aligned and perpendicular to a substrate in a dc discharge.