The effects of the particle size on combustion characteristics of pulverized coals under O-2/N-2 and O-2/CO2 atmospheres were compared using thermo-gravimetric analysis method. The results show the effect is greater in O-2/CO2 atmosphere. It presents obvious fluctuation, which becomes greater as the volatile matter content of coal increases. The effects of O-2 concentrations were also compared. The results show a noticeable discrepancy between O-2/N-2 and O-2/CO2 atmospheres at a low O-2 concentration and indiscernible at a high O-2 concentration. Meanwhile, the fluctuation effect is different under the different O-2 concentrations, which can be related to the reaction rate. In conclusion, under the O-2/CO2 atmosphere, the effect of the particle size on pulverized coal combustion is completely different from that under O-2/N-2 condition. (C) 2014 Elsevier B.V. All rights reserved.