The expansion of free bubbling gas fluidized beds has been investigated experimentally in a two-dimensional perspex-walled bed. Glass beads were fluidized with dried air at varying gas velocities, while the bed was vibrated at different frequencies, amplitudes and directions to study their effects on the fluidization quality. The experimental results showed that the particle flow pattern depends on the vibration direction, especially at superficial gas velocities less than the minimum fluidization velocity U-mf. The effect of horizontal vibration on fluidization behavior of glass beads exists at superficial gas velocities less than U-mf, while the effect of vertical vibration on fluidization behavior still exists even at higher superficial gas velocities than U-mf.