Disposal of anthropogenic CO2 in the ocean has been considered as a method to counteract global warming. A desirable method of the ocean disposal is to convert the less dense liquefied CO2 into denser CO2 hydrate via a submerged hydrate crystallizer at a depth < 500 m. The fate of CO2 hydrate in the ocean has been investigated. It is shown in this study that hydrate particles released in the ocean are physicochemically unstable; however, hydrate decomposition occurs only as a surface phenomenon. Because CO2 hydrate is denser than seawater, hydrate particles will sink in the ocean. During the descending process, the hydrate particles dissolve gradually in seawater owing to decomposition occurring continuously at surfaces of hydrate particles. This dissolution fate of CO2 hydrate in the ocean is significantly different from the previous prediction that the disposed CO2 hydrate would exist as a long-lasting entity in the ocean.