Minimum gas fluidizing velocity, fluidized phase expansion and porosity, fluidizing gas pressure drop, gas terminal velocity were experimentally determined at the fluidization of fines within voids of bed packed of spheres. Dependencies of those aerodynamic characteristics of the system on its geometric-dynamic parameters were investigated and appropriate empirical correlations were formulated. Investigations were performed with fines belonging to group B according to commonly accepted classification proposed by Geldard [15]; the applied fines were irregular in shape with course surfaces (sands) and spherical with smooth surfaces (glass ballotini).