This paper deals with the numerical analysis of kinematic and dynamic similarities of particle behavior in high shear mixer granulators with different vessel sizes. The three-dimensional particle motion in high shear mixer granulators with four different vessel sizes was calculated using a discrete element method (DEM). The geometrically similar mixer granulators equipped with a flat-shaped impeller blade were used as simulated mixer granulators. Kinematic and dynamic similarities of particle behavior in various vessel sizes under a constant normalized agitation power were numerically analyzed. In various vessel sizes, dynamic similarity expressed by the particle collision energy was confirmed under a constant normalized agitation power, while kinematic similarity expressed by the particle velocity was not confirmed. These results indicate that the dynamic similarity should be maintained for successful scale-up of high shear mixer granulators. (C) 2009 The Society of Powder Technology Japan. Published by Elsevier B.V. and The Society of Powder Technology Japan. All rights reserved.