Dispersion behaviors of fluidized particles have been investigated in a gas-liquid countercurrent fluidized bed of 0.152 m ID and 2. 5m in height. Since the dispersion flow of particles is highly irregular, stochastic analysis has been employed to analyze the behavior of dispersion characteristics. Pressure drop fluctuations have been measured and analyzed with the variation of time after change of the gas flow rate as a step function. Effects of gas and liquid velocities and particle kind (density) on the dispersion coefficient, fluctuating frequency and exiting rate of particles from the test section have been determined. It has been found that the dispersion behavior of particles can be classified into two states, heterogeneous and homogeneous expansion states, before it finally reached a new steady state. The dispersion coefficient and fluctuating frequency of particles increase with increasing gas or liquid velocity. The values of DP and F in the beds of relatively higher density particles(PE) are higher than those of relatively lower density particles(PP). The values of D_P and F have been well correlated in terms of dimensionless groups.