The change in the size of iron nanoparticles before and after single-walled carbon nanotubes (SWNTs) growth was systematically investigated for the first time using atomic force microscopy and transmission electron microscopy. In contrast to the conventional growth model of SWNTs, we found that thin SWNTs grow from large catalytic nanoparticles and all particles are finally embedded in SiO2 substrates after thermal chemical vapor deposition. The present results provide useful information for achieving diameter-con trolled growth of SWNTs. (c) 2006 Elsevier B.V. All rights reserved.