We formed An nanoparticles of 5 nm or less in diameter in the cavity of apo-ferritin (Au-ferritin). The Au nanoparticle in Au-ferritin exhibited catalysis for the synthesis of single-walled carbon nanotube (SWCNT) by chemical vapor deposition on various substrates. One-to-one correspondence of the grown SWCNT and the Au catalyst was confirmed by scanning electron microscopy (SEM) utilizing the high secondary electron yield of Au. In SEM images, it was possible to distinguish the SWCNT growth modes from metal catalysts, whether the catalyst particle was at the growth front or root, by placing Au-ferritin particles in a specified area. (C) 2007 Elsevier B.V. All rights reserved.