To understand three-dimensional dispersion of particles in the flow around a bluff body, direct numerical simulations of particle-laden wakes of a circular cylinder with Reynolds number ranging from 140 to 260 were performed. The domain decomposition method and high-order finite-difference schemes were applied to solve the fluid flow. A Lagrangian tracking solver was developed to trace the trajectories of each particle in the non-uniform grid system. It is observed that the predicted coherent structures and vortex dislocation frequency agree well with those of previous experimental studies. Particles at low Stokes numbers follow the vortex motion and can disperse into the core regions of the vortex-street and the recirculating region. Particles at larger Stokes numbers try to maintain their own motion, but take on a non-uniform distribution in the wake due to the strong folding effect of shed vortices. But for particles at intermediate Stokes numbers, higher concentration occurs in the outer boundary regions of the vortices as well as the thin band regions connecting adjacent vortex structures. Besides the spanwise vortex structures, the streamwise vortex tubes also have a remarkable effect on particle dispersion, which results in a 'mushroom' shape particle distribution in the wake. Furthermore, non-uniform forcing at inlet has additional effect on particle dispersion and mixing. (C) 2008 Elsevier Ltd. All rights reserved.