Bending deformation of an ionic conducting polymer-metal composite (a platinum plated Nafion) upon applied low electric field across its thickness is dominated by internal water redistribution. Internal water redistribution is associated with two phenomena, electroosmosis of hydrated ions and self-diffusion of free water molecules. Two processes can be considered separately in the way that fast electroosmosis is followed by much slower self-diffusion. Consequently, there is strain distribution due to different water content throughout the thickness. In the present study, finite element formulation is conducted for the basic field equations governing electrochemical-mechanical response of a platinum plated Nafion actuator upon applied electric field. Some numerical studies are carried out in order to show the validity of the present formulation.