The interaction of SO2 with the yttria-stabilized zirconia (YSZ) (111) and oxygen-enriched YSZ (111) (YSZ+O) surface is investigated using the first-principles method based density functional theory (DFT). It is found that SO2 is adsorbed either as a molecule or forms SO2鈭?/sup>3 species with new SO bonds to a surface oxygen on the YSZ (111) surface. In addition, there exist other species, e.g., SO3 and SO2鈭?/sup>4 on the very active YSZ+O (111) surface. Using the ab initio atomistic thermodynamics method, we present a detailed analysis on the stability of the SO2YSZ/YSZ+O system as a function of the ambient conditions.