Atomic Force Microscopy (AFM) has been used for the characterization of nanometric particles produced in rich flames. Very small particles (about 2 nm) have been found in pre-inception region of soot forming premixed flames, whereas both small nanoparticles as well as large soot particles have been found in the soot region of the flames. The smaller particles are very flat in shape if compared with the bigger ones, and this probably depends upon the different nature of the collected particles. Particle size distribution functions are reported for different sampling conditions. The results of AFM measurements are in good agreement with previous measurements performed with ultraviolet (UV) light scattering/extinction technique on the same flames. (C) 2003 The Combustion Institute. All rights reserved.