Dense carbon dioxide is an environmentally benign solvent, but its non-polarity limits the use of carbon dioxide as a reaction medium for electrochemical reactions. We have previously reported that the electrochemical polymerization in a carbon dioxide-in-water (CAV) emulsion proceeds to form conductive polypyrrole films [Jikei M, Saitoh S, Yasuda H, Itoh H, Sone M, Kakimoto M, et al. Polymer 2006;47:1547-54]. In this study, the effect of reaction conditions of the electrochemical polymerization on the resulting polypyrrole films was systematically investigated in order to reveal the features, flexibility and limitations of the C/W emulsion as a medium for electrochemical reactions. Other monomers, such as aniline and 3,4-ethylenedioxythiophene, were also examined for the electrochemical polymerization in the C/W emulsion. We have found that water-soluble monomers, such as pyrrole and aniline, are suitable for the electrochemical polymerization in the C/W emulsion that form films with a fine uneven texture. (C) 2007 Elsevier Ltd. All rights reserved.