In this study, the fluidization behaviors of the superfine particles with the mean diameter of 5.181 mu m were studied. The bed collapse experiment was conducted to study the fluidization quality and regime. The minimum fluidization velocity based on the agglomerate was determined. The agglomerate size distribution characteristic was studied by the 2D Particle Image Velocimetry (PIV). The agglomerate voidage was measured and discussed. The results showed that the micro-particles can also be fluidized in the agglomerate particulate fluidization regime like the nano-particles. The minimum fluidization velocity based on the agglomerate is 3.4 cm/s and much larger than that based on the primary particle. The agglomerate size has the multi-scale characteristic. The distribution of agglomerate diameter is in subject to the Gaussian distribution. And there exists the minimum agglomerate diameter under the effect of van der Waals cohesive force. The agglomerates in different sizes and shapes may have the similar particle arrangement structure. The measured averaged agglomerate voidage is 0.966. It may have an important effect on the interaction between the gas and agglomerate phases. (C) 2014 Elsevier B.V. All rights reserved.