In this study, multiwalled carbon nanotubes (MWNTs) were purified by using chemical method with different proportion of nitric acid and sulfuric acid liquid phase mixture. Carboxyl groups and other functional groups could be modified on the MWNTs surface. However, oxidation can damage the structure of carbon atoms on the surface of the carbon nanotube. Furthermore, the characteristic properties of MWNTs specimens were demonstrated by Raman spectrograph and Fourier transform infrared spectrum. The thermal properties and morphology of MWNTs were checked by Thermogravimetric analysis and Scanning electron microscope. (c) 2007 Wiley Periodicals, Inc.