Cyclic voltammograms of the aqueous solution containing polyammonium cations and the [Fe(CN)6]4-. anion at a plastic-formed carbon or platinum electrode were recorded. Polyammonium salts comprising quaternary ammonium in the main chain or sub chain and those comprising primary ammonium were tested. Under certain conditions, well-developed anodic and cathodic peak currents with the midpoint potentials different from that when the polyammonium cation is absent, that is, the midpoint potential of [Fe(CN)6]3- + e- = [Fe(CN)6]4- were exhibited, indicating that the [Fe(CN)6]4-/3- anionic species associate with the polyammonium cations tested to form the polycation-[Fe(CN)6]4-/3- complex species. The polycation complex species can be easily localized around the electrode surface with a dialysis membrane. An application of the polycation complex species as an electron-transfer mediator in the catalytic electrode with a redox enzyme was examined.