The results obtained studying the binding efficiency of different ashes,formed at Estonian Power Plant (EPP) and in the fluidized-bed combustion facilities towards CO2 and SO2, and the possibilities of activation of these ashes are presented. Experiments were carried out with thermogravimetric equipment at isothermal conditions in the temperature range of 400-800 degreesC in the atmosphere of CO2-air (+/-H2O) or SO2-air mixture. Chemical, X-ray diffraction, IR spectroscopy, BET nitrogen dynamic desorption, and other methods were used for characterizing the initial samples and the products of experiments. The CO2- as well as SO(2-)binding efficiency of ash samples taken front EPP was quite poor without preliminary activation. The best binding occurred at 750-800 degreesC. After a 5-min contact between solid and gaseous phases (at CO2 or SO2 partial pressure 190 mmHg) 0.06-0.12 mmole CO2 or 0.10-0.15 mmole SO2 was bound per 100 mg sample depending on the kind of ash. Preliminary activation of the samples increased their binding capacity towards CO2 and SO2 up to 2.2 and 3.8 times, respectively, reaching the level of binding efficiency of ashes formed in fluidized-bed conditions. The results of these studies confirm that the reactivity of oil shale ashes at binding acid gases greatly depends on ash formation conditions as well as on the binding conditions and preliminary activation of ashes.