The dissolution rate of liquid in CO2 in seawater, when a CO2 clathrate-hydrate film exists at the interface, is a key factor for estimation of CO2 sequestration in ocean and marine environmental impact assessment. Liquid CO2 dissolution phenomena in CO2 sequestration in the ocean include (i) dissolution and diffusion of liquid CO2 droplets at intermediate sea depths and (ii) CO2 dissolution in undercurrent flows from a liquid CO2 pool at seabeds deeper than 3000 m. For the first case, the present paper presents a data base of clathrate-hydrate covered CO2 droplet surface concentration, which is essential for an analysis of CO2 droplet dissolution behavior. Effects of pressure and temperature are included. A numerical simulation for dissolving liquid CO2 droplets released at an intermediate ocean depth is presented. The effects of released droplet size and ambient CO2 concentration on dissolution behavior are clarified. For the second case, an experiment simulating dissolution of liquid CO2 stared at a seabed into an undercurrent flow was conducted. The pool surface was covered with clathrate and the surface concentration of the clathrate-covered CO2 pool was estimated. Applying the measured surface concentration and mass transfer coefficient obtained from the actual conditions of deep ocean data, the time scale of CO2 dissolution into an undercurrent how was estimated, which is important for estimation of CO2 disposal in the deep ocean.