Unsteady three-dimensional simulation of interactions between uniform flow and fixed identical two particles is performed for particle Reynolds number 30, 100, 200 and 250. The drag force of interactive particles depends on Reynolds number as well as the inter-particle distance. They are attenuated when particles are aligned streamwise, augmented when they are held side by side against the mean flow. These are compared with available experimental data. Existence of periodical double-sided vortex shedding at relatively low Reynolds number is observed when particles are almost touching. The method adopted in this paper is not only simple and easy, but also accurate with a proper resolution. (C) 2003 Elsevier Ltd. All rights reserved.