Characteristics of gas-liquid volumetric mass transfer has been investigated in a riser of three-phase circulating fluidized bed(0.102 m ID and 3.5 m in height). Effects of gas(0.01-0.09 m/s) and liquid(0.12-0.43 m/s) velocities, solid circulation rate(2-8 kg/m(2)s) and fluidized particle size(1.0-3.0 mm) on the volumetric gas-liquid mass transfer coefficient have been examined. The mass transfer coefficient has been recovered from the concentration profile of dissolved oxygen in the axial direction of the riser by means of axial dispersion model. Tap water, filtered and compressed air and glass bead whose density is 2,500 kg/m(3) were employed as a liquid, gas and solid phase, respectively. It has been found that the gas velocity is a important factor to determine the value of mass transfer coefficient; the mass transfer coefficient increases with increasing gas velocity but it dose not change considerably with the variation of liquid velocity in the beds of relatively large particle(d(P): 1.7-3.0 mm), although the k(L)a value increases slightly with increasing U(L) in the beds of 1 mm glass bead. The value of mass transfer coefficient increases with increasing solid circulation rate as well as particle size. The mass transfer coefficient has been correlated as a function of operation variables as well as dimensionless groups.