Experiments have been carried out to study the effect of column internal diameters on fluctuation and expansion ratios. Three cylindrical columns with internal diameters as 0.099, 0.127 and 0.1524 m have been used to predict the effect of column diameters on fluctuation and expansion ratios. Factorial design (statistical approach) has been developed to predict fluctuation and expansion ratios in a gas-solid fluidized bed with varying gas-flow rates, internal column diameters and static bed heights. The values of fluctuation and expansion ratios predicted using the developed model have been found to agree well with the corresponding experimental ones. Columns with larger internal diameters give less fluctuation in the lower mass velocity range (G(f) < 2.5 G(mf)) and vice-versa. The expansion ratio bears an inverse relation with the column internal diameter.