The characteristics of SOx emission were investigated using SM (India) coal and Berau, C&A (Austria) coal. Experiments were performed in two different ways. In the first type of experiment, the temperature in the furnace was increased and the, samples were combusted at the ignition temperature after filling the furnace with coal. The second experimental method was to add the coal to after maintaining a constant temperature. The results demonstrated that SOx emission from coal combustion depended upon the sulfur content. In the case of Berau coal and C&A coal, an enhancement of combustibility which was accomplished by increasing the combustion temperature, an increase in airflow and decrease in particle size of coals tended to increase SO2 generation. Conversely, in the case of SM coal, the concentration of SO2 tended to decrease, because the high contents of Fe2O3 in the ashes increased the oxidation power of coal itself, which oxidized SO2 into SO3. In the case of C&A coal, the SO2 peak was only observed twice. This was thought to be caused by the thermal transfer rate from the surface to the interior of the coal.