The composite of polyaniline (PANI) and multiwall carbon nanotube carboxylated. through acid treatment (c-MWCNT) was synthesized by chemical oxidative polymerization in an inverse emulsion system. The resultant composites were compared with products from aqueous emulsion polymerization to observe the improvements in electrical conductivity, structural properties, and thermal stability obtained by this synthetic method. Prior to the inverse emulsion polymerization, MWCNT was treated with a strong acid mixture to be functionalized. with carboxylic acid groups. Carboxylic acid groups on surfaces induced selective dispersibility between polar and nonpolar solvents because of the increase of hydrophilicity. As the content of c-MWCNT was increased, the electrical conductivity was increased by a charge transport function from the intrinsic electrical conductivity of MWCNT and the formation of a highly ordered dense structure of PANI molecules on the surface of c-MWCNT. The images observed with electron spectroscopy showed the capping of c-MWCNT with PANI. The growth of additional ordered structures of PANI/c-MWCNT composite, which was observed through wide-angle X-ray diffraction patterns, supported the capping by PANI. It was observed that the doping of the composite had a significant relationship with the concentration of dodecylbenzenesulfonic acid (DBSA). The thermal stability of PANI composite was improved by the addition of c-MWCNT; this was thought to be related with structure ordering by inverse emulsion polymerization. (C) 2008 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 46: 2255-2266, 2008