The influence of solvent composition on the electrochemical properties of electrodes modified with [Os(bipy)(2)(PVP)(10)Cl]Cl films, where bipy is 2,2’-bipyridyl and PVP is poly(4-vinylpyridine), is investigated. The addition of acetonitrile or methanol to aqueous LiClO4 electrolyte solutions, greatly alters their electrochemical behaviour. The apparent diffusion coefficient for homogeneous charge transport (D-CT) has been evaluated using cyclic voltammetry and chronoamperometry. The charge transport rate is enhanced upon the addition of 5-60% of these solvents. Thermodynamic parameters evaluated for the charge transport process suggest that, upon polymer swelling, the rate limiting process changes from ion movement to polymer chain motion. This behaviour is interpreted in terms of the more facile transport of charge compensating counterions because of increased swelling of the layer in the presence of organic solvent.