Research on IS process, thermochemical cycle for hydrogen production by water-splitting process, are proceeded to utilize heat from High Temperature Gas-cooled Reactor as primary heat source. So far, the continuous hydrogen production of IS process on laboratory-scale have been successfully demonstrated through stable rate (1 liter per hour) of hydrogen production for 48 hours and stoichiometric production of hydrogen and oxygen. Further studies in three fields, the evaluation of materials in corrosion environments, the modification of HI processing scheme using membrane technologies and the art to operate closed-cycle process, are conducted. Aiming to investigate operational technique on IS process, a scaled-up glass plant is under construction; the plant has ability to produce hydrogen at a rate of 50 liters per hour and higher iodine concentration to separate solutions well.