The axial concentration distribution of the hydrophilic and hydrophobic particles, corresponding to poor and good attachment to rising bubbles in water, was investigated in a gas-liquid-solid fluidized bed. The sedimentation-dispersion model depicted satisfactorily the axial distribution of solids holdup by modifying only the terminal settling velocity, which considered the effect of an additional drag force resulting from the attached rising bubbles. This model explained correctly the different phenomena, i.e. solids holdup decreased with increasing the axial height in the non-attached system, but increased in the attached system.