This paper presents a numerical study of a dilute gas-particle flow in a 900 bend by employing a Lagrangian particle-tracking model combined with a particle-wall collision model and a stochastic wall roughness model. The major objective of this study was to investigate the effects of wall roughness on the particle flow properties. The numerical simulation revealed that wall roughness significantly reduced the 'particle free zone' and smoothed the particle number density profiles by altering the particle rebounding behaviours. It was also found that wall roughness reduced the particle mean velocities and also increased the particle fluctuating velocities in both streamwise and transverse directions. (C) 2007 Elsevier Ltd. All rights reserved.