A magnesium oxide/water chemical heat pump was examined experimentally as a heat storage system. A packed bed reactor of a magnesium oxide/water chemical heat pump was operated under various conditions. The heat storage and output performances of the heat pump were discussed. The heat pump is capable of being an alternative system of common water sensible heat storage because of the high-energy storage density of the heat pump. The heat pump containing the reactor is expected to enhance the energy utilization efficiency of a cogeneration system.