Nafion(R) coatings on electrodes are loaded with [Os(bpy)(3)](2+) and subjected to electrochemistry. Mass transfer and rheological changes during those processes are studied by using a quartz crystal resonator and phase-measurement interferometric microscope. In the loading process, the coating soaked in a [Os(bpy)(3)]ClO4 aqueous solution is once swelled with water and then gradually shrunk as protons in Nafioni(C) are exchanged with [Os(bpy)(3)](2+). Upon the first oxidation of [Os(bpy)(3)](2+) coupled with two sulfonate groups, acetate may be temporarily injected into the coating with water molecules to maintain electroneutrality, then [Os(bpy)(3)](3+) presumably reforms an ion pair with three sulfonate groups, ejecting surplus [Os(bpy)(3)](3+) coupled with three acetate ions. In the steady-state redox reaction, the rheology of the coating changes.