Several methods have been used to introduce sulfur containing groups in glass fiber supported activated carbon fibers (ACFs). The chemical and physical properties of these sulfur treated ACFs have been evaluated to determine their mercury adsorption capacities. Although sulfur impregnations decreased surface area and pore volume of ACFs, Hg uptake capacities increased when compared to raw ACF samples. For our sulfur-treated samples, sulfur atoms were incorporated into the carbon matrix in the form of sulfide and sulfate. The sulfide groups appeared to be more effective for mercury removal than sulfate. A possible mechanism for mercury adsorption, which is likely to involve the oxidation process of Hg degrees, is also discussed. Besides the effects of chemical structure on mercury adsorption, the effects of pore properties associated with adsorbents have also been studied. (C) 2013 Elsevier Ltd. All rights reserved.