The effect of collisions on the particle behavior in a fully developed turbulent flow in a straight square duct at Re-r = 300 is numerically investigated. The hydrodynamic modeling of the fluid phase is based on direct numerical simulation. The kinematics and trajectory of the particles as well as the collisions are described by the discrete element method. Three sizes of particles are considered with diameters equal to 50 mu m, 100 mu m and 500 mu m. Firstly, the particle transportation by turbulent flow is studied in the absence of the gravitational effect. It is found that the collisions play an important role in the particle distribution especially in the near-wall regions. The inter-particle collisions enhance the particle diffusion in the direction perpendicular to streamwise flow and make the particles distribute more uniformly near the wall. Then, the particle deposition is studied under the effect of the wall-normal gravity force in which the influence of collisions on the particle resuspension rate and the final stage of particle distribution on the duct floor are discussed, respectively. The collisions are found to have influence on the particle resuspension rate near the duct floor whereas hardly affect the particle behavior near the duct center. Under the gravitational effect the 50 mu m particles deposit more efficiently near the side walls but the 100 mu m and 500 mu m particles preferentially deposit near the center of the duct floor. Moreover, all the sizes of particles tend to concentrate near the center of the duct floor at the final stage of the particle deposition when the inter-particle collisions are considered. (C) 2014 Elsevier B.V. All rights reserved.