The nanocomposite films of polypyrrole (PPy) and multiwalled carbon nanotubes (MWCNT) were electrochemically synthesized by direct oxidation of pyrrole in 0.1 M aqueous solution of dodecylbenzene sulfonic acid containing a certain amount of MWCNT. The morphology, electronic conductivity, and thermal stability of the composite films have been studied by scanning electron microscopy, Raman spectroscopy and thermal gravimetric analysis. It was found that the mixing sequence of the surfactant, the monomer and MWCNT strongly influenced the compositions and thermal stability of the composite films. Raman spectroscopic studies indicated that the contents of the oxidized species of PPy in the composite films decreased faster than that of the neutral species during the heating process. The conductivity of each composite film showed a maximum in the temperature scale of 120-180 degreesC and then decreased dramatically with the increase of temperature. (C) 2004 Elsevier B.V. All rights reserved.