The holdups of two kinds of bubbles such as relatively large and small bubbles have been discriminated and investigated in a viscous three-phase (gas/liquid/solid) fluidized bed having a diameter of 0.102 m (i.d.) and height of 2.5 m, respectively. Effects of gas (U-G) and liquid (U-L) velocities, particle size (d(P)), and liquid viscosity (mu(L)) on the holdups of relatively large and small bubbles are determined. The holdups of two kinds of bubbles are estimated by means of the dynamic gas disengagement method combining with the static pressure drop method. The increase in the slope of pressure drop with a variation of elapsed time was quite different from each other between the two kinds of bubbles. It has been found that the holdup of relatively large bubbles increased with increasing gas velocity but decreased with liquid velocity and liquid viscosity. However, the holdup showed a local minimum with a variation of fluidized particle size. The holdup of relatively small bubbles increased with an increase in the gas velocity or solid particle size, but decreased with an increase in the liquid velocity or viscosity. The holdups of two kinds of bubbles are well correlated in terms of operating variables within these experimental conditions, respectively.