The effects of operating conditions on agglomerate sizes of SiO2, TiO2 and ZnO nano-particles were systematically investigated in a vibro-fluidized bed (VFB). The experimental results showed that slugging and channeling of bed disappeared, and the minimum fluidization velocity and the measured agglomerate sizes were decreased, resulting in the fluidization quality improving significantly due to introduction of vibration energy. A model to predict the agglomerate sizes was developed on the basis of energy balance among the agglomerate collision energy, the effective energy arising from vibration wave, energy generated by hydrodynamics shear and cohesive energy. Both of the experimental and theoretical results showed that vibration led to a smaller agglomerate size, and the average agglomerate sizes predicted by this model were in well agreement with those determined experimentally under conditions created in VFB. (C) 2012 The Society of Powder Technology Japan. Published by Elsevier B.V. and The Society of Powder Technology Japan. All rights reserved.