Numerical simulations were performed of a turbulent gas-particle multiphase flow in a circulating fluidized bed riser using a hard-sphere discrete particle model (DPM) for the particle phase and the Navier-Stokes equations for the gas phase, where the subgrid scale stresses (SGS) were modeled with the SGS model proposed by Vreman.(1) The model enables the simulation of systems with an arbitrary particle size distribution. In this work, binary mixtures of particles with different diameters were studied. From the numerical results it is found that the particles display size distribution in both horizontal and vertical directions. Small particles have a higher vertical particle velocity than the large particles. With increasing superficial gas velocity, the vertical particle velocity is increased. The average particle velocity and concentration vary both in the horizontal and vertical directions. Finally, the numerical results are compared with the experimental and numerical results of Mathiesen et al.,(2) It is found that the simulation results with Vreman's SGS model agree better with the literature data than those obtained with a classical Smagorinsky(3) model, especially in the zone close to the wall.