Carbon-based adsorbents with controlled porosity were prepared to investigate the adsorption capacity of refractory sulfur compounds. The porosity of carbon-based adsorbents was controlled by thermal treatment at 1173 K in CO2 environment. The equilibrium sulfur adsorption capacities of each adsorbent were measured for both model and commercial diesel. Pore widening of carbon-based adsorbents by CO2 activation increased BET surface area, total pore volume, micropore volume, and sulfur adsorption capacity. However, the sulfur adsorption capacity did not increase linearly according to the increase of BET surface area, total pore volume, and BJH pore volume, which included the properties of meso- and macropores. Specific micropore volume, whose pore diameters range from 0.63 to 1.2 nm, showed good linear relationship with sulfur adsorption capacity for commercial diesel. Model diesel adsorption tests supported that adsorbents with proper pore size for target sulfur molecules should be prepared for the enhancement of sulfur adsorption capacity.