A commercial activated carbon (Calgon OLC plus 12X30) was modified by oxidation and impregnation methods. The capacities of the resulting sorbents to adsorb tetrahydrothiophene (THT) were evaluated by conducting breakthrough tests. Carbon modified by oxidation with 50% HNO3 solution followed by impregnation with 1.05 mmol FeCl3 per gram sorbent displayed the greatest improvement in THT capacity, increasing from 0.9 mg S per gram of the parent activated carbon to 6.4 mg S per gram of the modified carbon sorbent. Effects of modification on surface physical and chemical properties were investigated using nitrogen sorption, scanning electron microscopy (SEM), and the pH detector. The results indicate that improving THT adsorption capacity is related to the surface acidity/basicity of carbon sorbents, i.e. increasing the acidic groups on the carbon surface improves THT capacity. The surface chemical properties play a more important role than physical properties (such as pore structure) in enhancing the sulfur adsorption capacity of the modified carbons. Impregnated metals also play important roles in THT adsorption and this effectiveness is related to increasing the number of acidic groups on the carbon surface.