Organic-inorganic composites composed of electrically conducting poly(3,4-ethylenedioxythiophene)/multi-walled carbon nanotube (PEDOT/MWNT) were prepared by in-situ oxidative polymerization of ethylenedioxythiophene (EDOT) in the presence of MWNTs in supercritical carbon dioxide. Prior to the polymerization, MWNTs were surface modified with 3-(trimethoxysilyl) propyl methacrylate in order to improve the dispersibility in CO2. This approach provides a facile way to develop solvent free composites with nanostructures and uniformity. The resulting composites were analyzed by FT-IR, transmission electron microscopy, field emission scanning electron microscopy, thermogravimetric analysis, X-ray diffraction and UV-visible spectroscopy. In addition, the effect of the ratio of the MWNT to PEDOT on the polymerization was investigated.