The use of an activated carbon (AC) with high ash content (15.92%) for SO2 removal was investigated during adsorption-desorption cycles. Significant deterioration in both dynamic and equilibria adsorption processes during the cycles was observed. To investigate the causes of deactivation, SO2 temperature-programmed desorption (SO2-TPD) experiments were conducted. The results indicated that most of the stored sulfur-containing species were released in the form of SO2 when the temperature was below 400°C. In addition to SO2, traces of CO were detected, but higher temperatures were required for the abundant release of CO. A Fourier-transform infrared spectrometry (FTIR) experiment was used to investigate changes in the oxygen-containing groups, and the results confirmed the formation of stable C-O complexes. These formations were tentatively attributed to the CO precursor’s occupation of active sites. Based on the formation of C-O complexes, two deactivation pathways in the cycles were proposed. The adsorption-desorption cycles also affected the AC ash. The formation of sulfur-containing species in the ash was confirmed through thermodynamic calculation and powder X-ray diffraction.