Cyclohexanol was oxidised to cyclohexanone in the presence of iodine and potassium iodide in a two layered solution composed of cyclohexanol and an aqueous solution on Pt-SPE prepared by an electroless deposition method of platinum on both surfaces of Nafion 415. Iodine species formed a mediatory system to accelerate the oxidation of the alcohol. The reaction efficiency was improved in the presence of iodine species. Only a small amount of I 2, 0.08 M, was enough as a mediator in an I 2 mediatory system, while the higher concentration, 1.7 M, was needed in the case of KI mediatory system. Iodine was observed as an intermediate in the KI system. Unipositive iodine species was considered as the oxidant in the mediatory systems. Water was advantageous in lowering terminal voltage up to about 30% without lowering the current efficiency. The current efficiency was lower than 30%. The reverse reaction of the oxidant in mediatory system was not important.