Supercritical carbon dioxide (SC-CO2) has been used to assist the preparation of conductive polypyrrole/cellulose diacetate (PPy/CDa) composites by in situ chemical oxidative polymerization. The morphology and conductivity of resulted composites were investigated with scanning electron microscopy and four-probe method, respectively. With the assistance of strong swelling effect of SC-CO2, composite films were obtained with a macroscopically homogeneous structure and conductivity up to 10(-1) S cm(-1) order of magnitude. Increasing the pressure of SC-CO2 increased conductivity, while increasing the temperature decreased conductivity. For comparison, PPy/CDa composite was also prepared with conventional oxidative method in aqueous solution. From the viewpoint of conductivity and environmental protection, the SC-CO2 method showed its superiority over the conventional one. (c) 2006 Wiley Periodicals, Inc.