Electrochemical redox reactions in a twin-electrode (TE) type cell composed of a couple of Nafion(R)-coated indium tin oxide (ITO) electrodes each incorporating Ru(bpy)3(2+) and methylviologen (MV2+) were analyzed by in-situ spectrocyclic voltammetry. The cell system, ITO/Nafion(R)[Ru(bpy)3(2+)]/aqueous electrolyte/Nafion[MV2+]/ITO, showed changes in visible absorption spectra induced by cyclic scanning of the potential difference between the two ITO electrodes. The spectral changes were attributed to the redox reactions of Ru(bpy)3(3+/2+) and MV2+/+. showing a multicolor electrochromism. The potential difference (+ 1.73 V) of the major redox wave in the cyclic voltammogram (CV) of the TE cell were close to the values (+ 1.76 V) calculated from the redox potentials of each species. Small peaks in the TE-CV suggested side reactions with H2O and 02, as well as migrations of the redox compounds into the opposite membranes. When each redox membrane was precycled repeatedly in an aqueous electrolyte solution, before fabricating a TE cell, the cell showed very stable behavior after repeated cyclic scanning. It has been shown that the present in-situ TE spectrocyclic voltammetry is useful for studying reactions occurring in practical devices.