Abstract: Electrodes coated with Nafion polymer films in which the cationic copper-bipyridyl complex(Cu(bpy)_2~(2+)) has been incorporated have been investigated by using XPS,ESR and cyclic voltammetric means. It is revealed that there exist considerably strong interactions between the incorporated species and the polymers, sulfonic sites,and that (at least) two kinds of environment are involved in the films. Much larger cyclic voltammetric response of the incorporated species (Cu(Ⅱ)←→Cu(Ⅰ)) is observed when a small amount of acid and/or, particularly, organic reagent which is electrochemically inactivei is added to the aqueous solution. The experimenatal results are explained by taking the different regions of Nafion into account. It is also preliminarily demon strated from cyclic voltammetry that the incorporated complexes in the polymer films exhibit electrocatalytic activity toward the reduction of dioxygen dissolved in the aqueous electrolyte.