The solid circulation rates of a binary mixture of ultrafine or superfine Al(OH)(3) powders and fluidized catalytic cracking (FCC) particles were investigated in a semi-batch circulating fluidized bed. The circulation rates were measured at different loadings of fine powders and different equilibrium water contents of the FCC particles. At a certain loading of ultrafine powders, the circulation rates were much smaller than in the presence of the superfine powders. The circulation rates were controlled by the strong cohesive property of the ultrafine powders, irrespective of the water contents of the FCC particles. Slight increases in the circulation rates were observed during fluidization of the ultrafine powders, even at higher equilibrium water contents of the FCC particles.