The effect of an air distributor on the fluidization characteristics of 1 mm glass beads has been determined in a conical gas fluidized bed (0.1 m - inlet diameter and 0.6 m in height) with an apex angle of 20°. To determine the effect of distributor geometry, five different perforated distributors were employed (the opening fraction of 0.009-0.037, different hole size, and number). The differential bed pressure drop increases with increasing gas velocity, and it goes from zero to a maximum value with increasing or decreasing gas velocity. From the differential bed pressure drop profiles with the distributors having different opening fractions, demarcation velocities of the minimum and maximum velocities of the partial fluidization, full fluidization, partial defluidization and the full defluidization are determined. Also, bubble frequencies in the conical gas fluidized beds were measured by an optical probe. In the conical bed, the gas velocity at which the maximum bed pressure drop attained increases with increasing the opening fraction of distributors.