Thermochemical water-splitting IS (iodine-sulfur) cycle produces the hydrogen from water using high temperature nuclear heat supplied by VHTR (very high temperature gas-cooled reactor). IS cycle is composed of three reactions; Bunsen reaction, sulfuric acid decomposition reaction and HI decomposition reaction. In KIER (Korea Institute of Energy Research), studies on the 2-liquid phase separation and purification, HI concentration form HIx solution (HI-I2-H2O mixture) by EED (electro-electrodialysis) and preparation of permselective membrane to use in membrane reactor for Bunsen reaction and HI decomposition reaction, respectively. Therefore a study on closed-loop cycle operation of IS cycle of 20µ¤/hr was carrying out. This paper presents result of the experiments conducting in KIER.