An electrochemically synthesised composite film, which consisted of poly(3,4-ethylenedioxythiophene) and poly(4-styrenesulfonate), was characterised by impedance spectroscopy and electrochemical quartz microbalance techniques in contact with aqueous electrolytes: LiCl, NaCl, KCl, CsCl. The influence of water flux on the ion transport measured as an excess of accompanied mass transfer changes in series: Li+ >Na+ >K+ >Cs+. Polymer ionic resistivity depends on the type of cations and changes such as: Li+ >Na+ K+, Cs+. The capacitance of the polymer was related to the type of cations pointing out caesium as the best co-ion.