The adsorption capacity with regard to SO2 of chars prepared from a low-grade coal has been evaluated at typical conditions of flue gas (presence of oxygen and water vapour and linear gas velocity of 0.12 m s(-1)) at an inlet concentration of 2 g SO2 m(-3). The flue gases have been simulated, varying the water vapour and oxygen contents as well as the adsorption temperature which was varied between 80 degrees C and 150 degrees C. The study has focused on the influence of several process variables as well as the intrinsic features of the chars, such as their porous texture, on the SO2 adsorption capacity of the chars. Under the conditions studied, the positive effect of water vapour in the absence of oxygen has been observed. This effect can be explained by the intervention of oxygen functionalities in chars. Here two effects overlap: the oxygen present in chars and their surface chemistry as well as the porous structure available. Temperature is also an important parameter in the SO2 adsorption efficiency. A minimum surface area is required for the temperature effect to be observed; otherwise the catalytic oxidation of SO2 to SO3 and subsequent storage of H2SO4 takes place to a very small extent and the negative effect of temperature increase to 150 degrees C is not appreciable.