Direct trajectory simulations have been carried out to investigate the growth mechanism of single-wall carbon nanotubes from the viewpoint of topological differences in the edge structure, i.e., zigzag or armchair, based on the semiempirical PM3 molecular orbital method. It is shown that the zigzag nanotube can grow smoothly if the zigzag is conserved form, while the armchair nanotube has a tendency to change into the chiral (or zigzag) form. These results agree with the static analysis of frontier electron density distributions in our recent reports as well as with the experimental observations of Sattler et al. (C) 2002 Elsevier Science B.V. All rights reserved.