Multi- walled carbon nanotubes ( MWNTs)/ polyaniline ( PANI) composite materials were prepared by in- situ chemical oxidative polymerization of an aniline solution containing well- dispersed MWNTs. The supercapacitive behaviors of these composite materials were investigated with cyclic voltammetry ( CV), charge - discharge tests, and ac impedance spectroscopy, respectively. The composites based on the charge- transfer complex between well- dispersed MWNTs and PANI matrixes show much higher specific capacitance, better thermal stability, lower resistance, and were more promising for applications in supercapacitors than a pure PANI electrode. The highest specific capacitance value of 224 Fg(-1) was obtained for the MWNTs/ PANI composite materials containing MWNTs of 0.8 wt%. The improvement mechanisms of the capacitance of the composite materials were also discussed in detail.