The single-wall carbon nanotubes (SWNTs) purified by nitric acid were ultrasonicated in monochlorobenzene solution. Thermogravimetric analysis complemented by transmission electron microscopy and Raman spectroscopy was used to analyze the thus ultrasonicated SWNTs. The results show that two kinds of modified SWNTs and one modification-free SANT coexist in ultrasonicated SWNTs and burned in three different temperature ranges. The different chemical modifications of SWNTs are likely to arise from their different structures. This provides a possible way to analyze and separate different structures of SWNTs. (C) 2002 Elsevier Science B.V. All rights reserved.