The formal standard rate constants for the redox systems, Fe(bipy) 3 3+/Fe(bipy) 3 2+,Fe(bipy) 2(CN) 2 −/Fe(bipy) 2(CN) 2, Fe(bipy)(CN) 4 −/Fe(bipy)(CN) 4 2− and Fe(CN) 6 3−/Fe(CN) 6 4− (bipy=2,2′-bipyridine), in aqueous solution and N,N-dimethylformamide solution are measured with the aid of the galvanostatic double pulse method. The standard rate constant decreases as the number of the coordinated 2,2′-bipyridine decreases. It is in accordance with the trend in the homogeneous rate constants for these systems and is interpreted on the basis of the extension of ligand π-orbitals. This finding may be evidence for the mechanistic similarity of the electrochemical electron-transfer reaction of a redox system to the corresponding homonuclear electron-exchange reaction occurring in solution phase. An empirical relation between rate constants for both kinds of reactions is discussed. It is noted that the maximum electrochemical rate constant is limited at a value much smaller than the one theoretically allowed.