An Euler-type gas/particle two-phase flow numerical model is presented for simulating the deposition of particles of tens of microns. At this size range of particles, the dominant effect considered for deposition on the bottom surface is gravitational settling. The mass conservation equation for the particulate phase is developed and simulated to include convection, diffusion, and gravitational settling effects. Experiments were conducted in a room-scale chamber by injecting nano-particle aggregates, and the deposition rates were measured using a specially designed sequential sampler. The measured deposition-rate data are compared with the simulation results for validations. Distributions of particle-number density at different times are plotted in several viewing planes to facilitate discussion of the particle-distribution patterns. The comparisons show that the agreement between the modeling and the measurement is best at the intermediate particle-size range. (C) 2009 The Society of Powder Technology Japan. Published by Elsevier B.V. and The Society of Powder Technology Japan. All rights reserved.