The role of thermal oxidation before acid treatment and post high-temperature vacuum annealing of single walled carbon nanotube (SWCNTs) was studied by scanning electron microscopy, high-resolution transmission electron microscopy, thermogravimetric analyses and Raman spectroscopy. An efficient procedure is developed for the purification of SWCNTs with minimal damage to the walls and minimal modification in the length of the tubes. SWCNTs are employed in this study, are synthesized by arc-discharge method containing impurity of amorphous carbon, carbon shells, graphitic particles, metallic nanoparticles and metallic nanoparticles encapsulated inside the amorphous carbon or graphite. (C) 2008 Elsevier BY. All rights reserved.