Behaviour of cohesive powders in a powder-particle spouted Bed (PPSB) has been investigated under several operating variables and solids properties. The elutriation rate constant based on the hold-up of fine powders in the bed decreased with a decrease in the size of fine powders, and with an increase in the size of coarse particles under a constant superficial gas velocity. This finding is quite different from the elutriation phenomena of particles more than 100 mum in size. Moreover, the mean residence time of fine powders increased with a decrease in the superficial gas velocity and the size of fine powders, and decreased with a decrease in the size of coarse particles.