The mixture of polyaniline (PANi) and PANi grafted multiwalled carbon nanotube (PANi-g-MWNT) was prepared by a two-step reaction sequence. MWNT was first functionalized with 4-aminobenzoic acid via "direct" Firedel-Crafts acylation in polyphosphoric acid (PPA)/phosphorous pentoxide (P2O5) medium to afford 4-aminobenzoyl-functionalized MWNT (AFMWNT). Then, aniline was polymerized via an in situ static interfacial polymerization in H2O/CH2Cl2 in the presence of AFMWNT in organic phase to yield the mixture of PANi and PANi-g-MWNT. The mixture was characterized with a various analytical techniques such as elemental analysis (EA), Fourier transform infrared spectroscopy (FTIR), wide angle X-ray diffraction (WAXD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), thermogravimetric analysis (TGA), cyclic voltammogram (CV), UV-vis and fluorescence spectroscopies, and electrical conductivity measurement. On the basis of TGA analysis, the thermo-oxidative stability of the mixture was markably improved compared to that of PANi homopolymer. Even after dedoping, in alkaline solution, the mixture would still display semimetallic conductivity (4.9 S/cm). The capacitance of the mixture was also greatly enhanced and its capacitance decay with respect to cycle times was significantly reduced. (C) 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 1962-1972, 2010