The present paper was addressed to ash particle formation during O-2/CO2 combustion of pulverized coal. Three typical Chinese coals were burned in a drop tube furnace to generate ashes under various combustion conditions. The residue ash particles were measured with Malvern technique. The fine ash particles collected by a low pressure impactor were subjected to the analyses of size distribution and elemental composition to study the fine ash formation. The impacts Of O-2/CO2 combustion on ash particle formation were explored through extensive comparisons between O-2/CO2 combustion and O-2/N-2 combustion. It was found that O-2/CO2 combustion did not significantly affect the size distribution of the residue ash particles but did significant affect the mass and composition size distributions of both the submicron particles and the fine fragmentation particles. Nevertheless, O-2/CO2 combustion did not change the formation mechanisms of the submicron particles and the fine fragmentation particles. (C) 2007 Elsevier B.V. All rights reserved.