Abstract: The fluidization characteristics or hydrodynamic behavior of nanoparticles (mixtures of 30 and 100 nm diameter particles) and microparticles (d_p = 75 μm) of Aluminum Oxide (Al₂O₃) were studied in a fluidized bed of a gas-solid system. Experiments were performed in two cylindrical columns the first column with a diameter of D = 4.3 cm and the second with a diameter of D = 7.1 cm by varying different system parameters (viz., static bed height, particle size and superficial gas velocity) using air as the fluidizing gas. Vibration technique was used for nanoparticle fluidization to avoid nanoparticle agglomeration. A simple analytical model is used to predict the agglomerate sizes for Al₂O₃ nanoparticles. The average agglomerate size was calculated using Stoke=s law and the minimum fluidization velocity was calculated using the Ergun equation. The minimum fluidization velocity was 0.0183-0.046 m/sec without vibration and 0.0163-0.033 m/sec with vibration in the column with D = 4.3 cm for different static bed heights (5, 10 and 15 cm). In the column with D = 7.1 cm, the minimum fluidization velocity was 0.025-0.05 m/sec without vibration and 0.022-0.037 m/sec with vibration for different static bed heights (5, 7 and 10 cm). In addition, the fluidization behavior for Al₂O₃ microparticles was studied and the minimum fluidization velocity was calculated using the Ergun equation. In this case, the minimum fluidization velocity was 0.034-0.050 m/sec for the column with D = 4.3 cm and 0.063-0.070 m/sec for the column with D = 7.1 cm. Fluidization characteristics such as the bed expansion ratio, bed fluctuation ratio, bed pressure drop and the Fluidization Index (FI) of nanoparticles are described and discussed. The calculated values for different fluidization characteristics are compared with the experimentally observed values. A comparison of the results shows consistency between the experimental and calculated values for nanoparticles.