This study was carried out to investigate the heat storage/release characteristics of the thermochemical reaction of the calcined dolomite with the packed bed shape experimental apparatus for development of chemical heat pump system. In the present study, it was found that MgO of the calcined dolomite was not hydrated during the hydration process under the experimental conditions. Therefore, the MgO of the calcined dolomite can be regard as an inert material. As a result, it was found that all of CaO packed kept the reaction temperature of about 510℃ through the entire part of the bed The dehydration reaction was incurred first at the wall side area as the supplied heat was transferred through the wall side into the packed bed As a result of the temperature and concentration spread, the reaction was completed at the wall side progressed into the center.