AbstractA redox reaction was mediated by polymeric membranes which contain naphthoquinone derivatives as electron and proton carriers. When such a membrane containing vitamin K1was placed between two aqueous solutions of potassium ferricyanide and sodium dithionite, the oxidation‐reduction of them took place, but the reaction was rather slow. Although vitamin K3was a more effective carrier and the reaction proceeded fast, the reaction rate decreased in the repeated runs. Since the reduced form of this carrier is slightly soluble in water, a part of the carrier got dissolved in the aqueous phase from the membrane during the reaction. 2‐Alkyloxy‐1,4‐naphthoquinones such as 2‐hexyloxy‐1,4‐naphthoquinone effectively transported electrons and protons through the polymeric membranes, promoting the membrane‐mediated reaction; in these cases no retardation was observed in th