Bidispersed mixts. of small and large Al(OH)(3) particles were fluidized to study the bed collapse. The effect of the particle mixture of A and C according Geldart classification on their hydrodynamic characteristics was analyzed. The min. fluidization velocity, bubbling velocity, settling time and collapse velocity of the bed were detd. Advantageous increase of the range of homogeneous fluidization and decrease of settling velocity were obsd. for mixts. with Hausner ratio 1.25-1.4. The formation of confined fluidized beds in mixts. with the extreme large grain diams. was also established.