Electrocatalytic proton reduction was studied using Ru-red ([(NH3)(5)Rn-III-O-Ru-IV(NH3)(4)-O-Ru-III(NH3)(5)]Cl-6) dispersed into a Nafion(R) membrane coated on a basal-plane pyrolytic graphite (BPG) electrode (denoted as BPG/Nf[Ru-red]) in a pH 1 electrolyte solution. It was found that the Nf[Ru-red] shows high activity in H+ reduction to produce H-2. The electrocatalytic reaction by Ru-red embedded in the polymer membrane started to take place by forming catalytically active species after irreversible change of the complex under cathodic conditions. Electrochemical features of the Ru-red in the membrane as well as electrocatalysis by the Nf[Ru-red] for H+ reduction were discussed based on the results of CV measurement, UV-Vis spectroscopy before and after the electrochemical process and potentiostatic electrolysis.