Coagulation is a process wherein aerosol particles collide with one another and adhere to form large particles in the system due to their relative motions. In this letter, we investigated thermophoretic coagulation of monodisperse aerosols on a constant temperature gradient between particles and gas molecules using a FDM (finite difference method) technique. The basic concept is to focus on a single particle attracting other particles considering their diffusional and thermophoretic motions to its collision surface. From the results of simulated particle flux, it shows that the thermophoretic coagulation is more effective for higher temperature gradient in the monodisperse aerosol particles. (C) 2010 Elsevier Inc. All rights reserved.