Electrochemical method can be useful for the determination of diffusion coefficients in various media. For low polarity media, ultramicroelectrodes are preferably used. In this work, the electro-oxidation of ferrocene has been studied in dimethylformamide (DMF)-CO2 mixtures under various CO2 pressures, using a 100 mu m diameter Pt microelectrode. Tetrabutylammonium perchlorate (TBAP) was chosen as the supporting electrolyte. Cyclic voltammetry was used in order to obtain values of diffusion coefficient of ferrocene, which were determined by using the Randles-Seveik relation. This method proved to be convenient in such low polarity solvent. In addition, fluid phase equilibria Of CO2-DMF mixtures were calculated and pressure-composition phases diagrams were established for the concerned binary mixtures, thanks to commercial Prophy Plus TM software (Prosim S.A., France). So, both liquid phase expansion, due to swelling by high-pressure CO2 and effective bulk concentration of ferrocene were estimated. Nevertheless, electrochemical measurements were problematic when high-pressure single phase conditions Of CO2-DMF mixtures were reached. (C) 2007 Elsevier B.V. All rights reserved.