The deposition of aerosol particles in laminar mixed-convection flow in a lid-driven cavity with two heated obstacles is investigated numerically by an Eulerian-Lagrangian method. Lagrangian particle transport calculations are carried out to track 2000 particles that initially exerted with random distribution in flow regime and also assumed that the effect of particles on the fluid is neglected. All the affecting forces on particle equation of motion, such as Brownian, thermophoresis, drag, lift and gravity are considered. The main goal is to study the effective parameter on deposition of particles such as free convection, distance and size variation of obstacles. Numerical results showed that free convection is an effective parameter that affected the deposition. As a main result, it is observed that deposition decreases with increasing in the Richardson number. Results showed that by increasing obstacles distance, deposition increases. Finally, it is revealed that the size of obstacles has a great effect on particle deposition, such that by increasing the obstacles size, the deposition increases. (C) 2011 The Society of Powder Technology Japan. Published by Elsevier B.V. and The Society of Powder Technology Japan. All rights reserved.