Previously we have reported that H2S reacts with iron oxide to form FeSx, which captures elemental Hg vapor (Hg0) as HgS. In this work, we studied the relation between the rate of Hg0 removal and the rate of sulfidation of iron oxide using a laboratory-scale fixed-bed reactor for the Hg0removal and thermo-gravimetric analysis (TGA) for the sulfidation of iron oxides in a temperature range of 60 to 100°C. Supported and unsupported iron oxides pre-Treated (dried and calcined) at various temperatures were utilized. The relationship between sulfidation and Hg 0 removal is not yet clear. The presence of CO in the feed gas suppressed the weight gain of iron oxide, however the Hg0 removal capacity was unaffected by the presence of CO. In the case of Fe 2O3--110 (dried at 110°C), generation of COS was confirmed during the removal of Hg0.