In order to understand particle response to turbulence along its path, properties of the particle phase and gas phase are compared and analyzed for a turbulent flow over a backward-facing step. The turbulent gas phase is simulated numerically using large eddy simulation and the particle phase is modeled by means of Lagrangian methods. The particle Stokes number ranges from 0.01 to 111.18 and the Reynolds number is 18,400, based on the step height and the inlet mean velocity. Particle velocities, fluid velocities and vorticity along particle trajectory as well as particle dispersion are obtained so as to provide information on particle response to turbulence. Results show that particle behavior depends heavily on the local fluid turbulence along its path, especially for small particles. Particles follow a path along which the gas-phase vorticity is small. However, large particles maintain the inertia along their trajectories without responding to the fluid fluctuations. (c) 2005 Elsevier Ltd. All rights reserved.