We have investigated the influence of the vacuum level upon the growth of carbon nanotubes (CNTs) on 6H-SiC (0 0 0 (1) over bar) surface. CNTs of about 160 nm in length were formed densely and uniformly on the 6H-SiC surface during annealing at 1700 degrees C in a high vacuum (similar to 10(-2) Pa). CNTs of about 1 mu m in length were formed during annealing at 1700 degrees C in an ultra-high vacuum (similar to 10(-7) Pa). However, CNTs were not formed and SiO2 layers were formed on the SiC surface at 1700 degrees C in air. It is found that longer CNTs can grow up in an ultra-high vacuum, moreover, a little aligned and low-density graphite layers, or carbon nanofibers can also grow up. (C) 2008 Elsevier B.V. All rights reserved.