The overall mass transfer coefficient between the bubble phase and the emulsion phase was measured at ambient temperature in a fine particle fluidized bed. The measurements were carried out using the absorption of carbon dioxide in air by porous alumina particles impregnated with an aqueous solution of NaOH. The pressure fluctuations and the ascending velocity of bubbles were also measured. The overall reaction rate was influenced by the mass transfer between the two phases and the fraction of particles in the freeboard at high gas velocity. The flow pattern of bubbles was discussed in relation to the surface area of bubbles calculated from the mass transfer coefficient and the bubble signals detected by optical probes.