This study investigated the effects of the inner structure of a centrifugal separator on particle classification performance. The typical inner structure of centrifugal separators is as follows: a blade, which consists of two orthogonal plates. is inserted into the centrifugal separator to create rigid fluid and particle rotations. The results of the present study demonstrate that centrifugal separator performance was significantly improved by attachment of a cylinder to the center of a conventional blade. Modification of the separator by attachment of the cylinder to the center of the centrifugal separator is expected to prevent the particles in the slurry from passing through the central axis of the centrifugal separator. Hence, the particles are subjected to greater centrifugal force. Both experimental and theoretical results demonstrate that particle classification performance increases as the cylinder radius increases. Thus, it is evident that attachment of a cylindrical blade to the center of the centrifugal separator allows for effective and highly efficient collection of extremely small-classified fine particles. (c) 2009 Elsevier B.V. All rights reserved.