The penetration of fine cohesive powders through a powder-particle fluidized bed (PPFB) was studied and correlated with the hold-up of fine powders in the bed. Silica sand, limestone, glass beads, bentonite, composite clay and silica gel of 550 gm mean size and silica sand of 780 mu m mean size were used as coarse particles. Aluminum hydroxide powders of 0.5, 1.0 and 3.0 mu m mean size were used as fine powders. The effects of aerosol concentration and size of fine powders, type of coarse particles and superficial gas velocity on the penetrating fraction of fine powders were investigated under various hold-ups of fine powders in the bed at the non-equilibrium state. In the early stage of penetration, the penetrating fraction of fine powders was hardly affected by the inlet aerosol concentration of fine powders, superficial gas velocity and size of coarse particles, but strongly affected by the size of fine powders and type of coarse particles. A fluidized bed of angular coarse particles having a rough surface or a highly rough surface with a granular structure demonstrated very low penetration of aerosol fine powders until relatively high hold-up of fine powders in the bed. Beds of coarse particles having a higher angle of repose gave higher equilibrium hold-up of fine powders in the bed.