JFE Engineering has developed clathrate hydrate slurry (CHS) for use in next-generation energy-saving air-conditioning systems. Clathrate hydrate slurry is suitable for cooling applications as it possesses latent heat in the range of 5-12°C, has a cooling storage capacity 2-3 times as large as that of the conventional chilled water, and displays excellent pumpability. Because CHS is a cooling medium with high thermal density, air-conditioning systems using CHS are expected to substantially reduce cooling medium transportation costs and make an important contribution to energy savings, with attendant benefits in reducing CO₂ emissions. This paper describes the properties of CHS and the results of a trial calculation of the energy-saving effect of an office building air-conditioning system using CHS.