The Nafion doped polyaniline blends are prepared by a one-step method based on the codissolution of a proton exchanged Nafion powder and polyemeraldine base in NMP. As determined by elemental analysis, the doping level of PAni is dependent on the number of sulphonate groups per aniline unit and reaches a maximum value of 0.4. TEM pictures reveal the electronic conducting polymer dispersion in the Nafion matrix. Ionic conduction and electronic transfers are examined by ne impedance spectroscopy. The dependence of the electronic conductivity of the material on the composition, the swelling rate and the temperature leads us to suggest the contribution to the bulk conductivity of transverse polarons and bipolarons stabilised by sulphonate groups.