Effect of fine particle addition on the fluidity of industrial catalyst was investigated. It was found that the fluidity depended not only on particle diameter and particle density, but also surface properties of particles. If the surface was smooth, even if they were Geldart's group A particles, slugging or channeling tended to arise in the bed. When fine powders of a diameter less than 2 mu m were added to poorly fluidizing catalyst particles by 0.015 wt%, the fluidity was drastically improved. This effect was considered due to lowering excessively strong van der Waals force acting between the A-type particles with smooth surface by the existence of fine powders adhering on the surface. It was found that the minimum quantity of the fine powders for improving fluidity depended on the size of the fine powders. The improvement was found continuing for several hundred hours at 0.2-0.4 m/s superficial velocity.