CO2 clathrate formation and its properties were measured using three kinds of test facilities. The biggest one has a capacity of 16.7 l and maximum operating pressure is 320 Kg/cm2. Main results are as follows; . Phase equilibrium data Of CO2 clathrate-sea water and CO2 clathrate-deionized water were obtained. . pH of sea water at high pressure and at various CO2 concentration were measured. . CO2 clathrate dissolution rate in sea water was measured. These experiments are being carried out under the joint research of TEPCO and IHI to confirm whether the ocean is suitable for CO2 stockyard.