There is an urgent need to understand sorbent tolerance for capturing carbon dioxide (CO2) in the presence of sulfur dioxide (SO2). Sulfur oxide is emitted together with CO2 from various combustion systems and can cause severe air pollution. In this study, the behavior of different dopants on the performance of calcium oxide (CaO) sorbent for capturing CO2 in the presence Of SO2 was investigated. Three main sets of experiments were carried out to study carbonation and sulfation both separately and simultaneously using a thermogravimetric analyzer (TGA). The results show that SO2 reduced the capability of the sorbents for capturing CO2 because of the competition between carbonation and sulfation reactions. Formation of calcium carbonate (CaCO3) and calcium sulfate (CaSO4) took place upon carbonation and sulfation, respectively. Our TGA and X-ray photoelectron spectroscopy (XPS) results indicate that the carbonation is totally reversible, while this is not the case with the sulfation. The permanent residual weight gained by the sorbents during the course of sulfation is attributed to the irreversible formation of sulfate species, which is confirmed by both the TGA and XPS results. The Ce promoted CaO sorbent exhibits the best performance for CO2 capture and is the most SO2 tolerant sorbent. On the other hand, the Mn doped dopant has the strongest affinity for SO2.