The soot formation process and the structure of a fuel-rich premixed flame stabilized in the downstream side of a porous medium have been investigated by experimental measurements and numerical analysis. In the numerical analysis, a modified Tesner's model for the reaction rate of soot formation has been introduced through a comparison between measured and calculated distributions of the temperature and the species mole fractions. Furthermore, a novel model for soot growth is developed, taking both surface and coalescence growths into account. On the basis of this model, the following results are obtained. Surface growth becomes dominant immediately after the beginning of soot formation. In the downstream side, the soot particle increases due to grow by the coalescence with smaller soot particles, and decrease as a result of collision with radicals and coalescence with larger soot particles. (C) 2004 Elsevier Ltd. All rights reserved.