Charge transport in a Nafion membrane incorporating a mu-oxobis[aqabis(2,2＇-bipyridine)ruthenium(III)] complex, [(bpy)(2)(H2O)Ru-O-Ru(H2O)(bpy)(2)](4+) [abbreviated to Ru-III(OH2)-O-Ru-III(OH2)], was studied by using a potential-step chronocoulospectrometry (PSCCS), The oxidation of Ru-III(OH2)-O-Ru-III(OH2) to Ru-III(OH2)-O-Ru-IV(OH) was observed on a potential-step from 0 V vs. SCE to 1.0 V in the PSCCS measurement. The charge transport rate, mu(CT), is remarkably depended on the complex concentration. The analysis showed that the charge propagation takes place by charge hopping, whose rate constant is dependent on the complex concentration. Charge hopping distance between the complexes in the membrane was analyzed to be 1.09 nm based on an intermolecular distance distribution between them.