At 250°C, the interactions between gaseous sulfur dioxide and nickel oxide have been investigated by means of the temperature-programmed desorption (TPD) and microcalorimetric techniques. According to the thermal treatment of the oxide, different NiO samples were prepared with different energetic chemisorbed oxygen species called O¹, O², O³ and O⁴. As indicated by our calorimetric data, weakly bound species O¹ seems to be the most reacive oxygen form with sulfur dioxide. In this case, the TPD curves (m/e 48 and 32) show a new peak at 710°C and it may be corelated with the desorption of a sulfur compound created by oxidation of sulfur according to the reaction S^IV ↔ S^VI.