Potential-step chronoamperospectrometry (PSCAS) was employed to investigate electron transport associated with redox reactions of the Ru(bpy)(3)(2+/3+) couple in a Nafion film. The electron propagation within the Nafion was found to take place through an electron hopping mechanism for the oxidation of Ru(bpy)(3)(2+) to Ru(bpy)(3)(3+), but by a physical diffusion mechanism for the reduction of Ru(bpy)(3)(3+) to Ru(bpy)(3)(2+). In the oxidation of Ru(bpy)(3)(2+), the electron transfer distance for the electron hopping and the bounded motion was estimated by modified Poisson statistics. The electron transfer distance, which includes the bounded motion and electron hopping distance, become longer on increasing the applied potential from 1.1 to 1.5 V (SCE) due to the increase of electron hopping distance (increase of the center-to-center distance from 1.13 to 1.47 nm). The bounded motion distance (0.25-0.31 nm) remained almost unchanged. The bimolecular rate constant for an electron transfer step also increased with increasing the applied potential. The apparent diffusion coefficient (D-app) for electron propagation during the reduction of Ru(bpy)(3)(3+) was 1.2 similar to 8 times larger than that measured for the oxidation of Ru(bpy)(3)(2+) under the same conditions.