Rate constants of the redox-electrode reaction for the Fe(CN)(6)(3-)/Fe(CN)(6)(4-) couple at platinum (111), (100) and (110) single crystal electrodes in 0.1 M KClO4 solution were obtained by ac impedance measurements. The rate constants were found to be largely dependent on the surface orientation, and increased along the series of (110) < (100) < (111). The results strongly suggest that the electron transfer process for the couple would not obey a simple outer-sphere mechanism. An in situ IR spectroscopic observation of each electrode surface in the solution containing 1 mM K4Fe(CN)(6) clearly indicated the presence of adsorbates ascribable to the cyanide group on every surface, and the spectral features on the (111) surface were found to be different from those on (100) and (110). The dependence of the rate constant at the (111) surface on the substrate concentration and the electrolyte cation was also investigated.