The present work was aimed at investigating particle size evolution during pulverized coal combustion in an O-2/CO2 atmosphere in comparison to that in an O-2/N-2 atmosphere. Two narrow size fractions of a bituminous coal were devolatilized in N-2 and CO2 and burned in O-2/N-2 and O-2/CO2 atmospheres in a high-temperature drop-tube furnace. The resulting chars and residual ashes as well as the parent coals were characterized with scanning-electron-microscopy-based image analysis to quantify particle size distributions, which were systematically compared. The results show that devolatilization in CO2 produces finer char particles than that in N-2. It may have a consequence on particle size evolution and ash particle formation during char conversion. Combustion in an O-2/CO2 atmosphere generally generates more fine ash particles than burning in an O-2/N-2 atmosphere at the same oxygen level. Increasing the O-2 concentration decreases the amount of the fine ash particles in both atmospheres. The results also show that changing gas atmospheres has a greater influence on the evolution of the particle size distribution during the combustion of the larger coal size fraction.