Sequestration of liquid CO2 into intermediate depth ocean has been considered as a means to reduce atmospheric concentration of this greenhouse gas and mitigate global warming. A number of CO2 droplets are released into ocean and are diluted. The CO2 solubility into sea water is very important in order to control the amount of released CO2 and environmental impact. Under conditions in the intermediate ocean, that is, high pressure and low temperature, the CO2 clathrate hydrate film was formed on the CO2 droplet surface. The hydrate film has been considered to decrease the dissolution rate and the CO2 concentration at the boundary layer on the droplet surface. In the experiments, LIF technique was used. The CO2 dissolved water emitted intense fluorescence, while the CO2 itself did not illuminate. Therefore, we could know the shrinking rate of CO2 droplet diameter accurately. The CO2 solubility was derived by using the measured shrinking rate. The solubility was investigated qualitatively with some variable parameters, i.e., pressure, temperature and salinity.