We have carried out an experiment on the interaction between concentrated particles (hereafter called the Cluster) and Karman vortices in solid-liquid two-phase flow. The Karman vortices have been obtained by moving a cylinder in a shallow towing tank. The density of the particle is nearly the same as that of liquid. We have adopted High-resolution PIV to distinguish the Cluster velocity from the vector field of the surrounding flow. From the obtained data, we conclude that the Clusters enhance the steady rigid body rotation of the Karman vortices and the flow along the vortices. Furthermore, the Clusters keep their rotational motion and do not follow the flow along the vortices completely. (C) 2003 Elsevier Science Ltd. All rights reserved.