Characteristics of unsteady state behavior and fluctuations of fluidized particles have been investigated by adopting the stochastic method in a three-phase fluidized bed of 0.152m ID and 2.5m in height. Air, water and glass beads whose density is 2500kg/㎥ and diameter is in the range of 1.0-6.0X10-3m have been used as gas, liquid and solid phase, respectively. The mean fraction, mean residence time and fluctuating frequency of fluidized particles in the test section, and the exiting rate of the particles from the test section have been obtained. The exiting rate of the particles has decreased exponentially with time lay during the relaxation of the bed, and the mean residence time of the particles in the test section has decreased with an increment of the gas velocity. The fluctuating frequency of particles has increased with an increment of the gas velocity and particle size, but it has attained its maximum value with an increment an increment of the gas velocity and particle size, but it has attained its maximum value with an increment of the liquid velocity and bed porosity. The particle fluctuating frequency has been well correlated in terms of dimensionless particle size and dimensionless fluid velocity based on the isotropic turbulence theory.