A series of sulfur-doped microporous carbon materials were prepared by directly using potassium hydroxide as the activating agent. The specific surface area and pore volume of the sample CKS-5 (activated at 800 degrees C for 180 min according to an alkali/carbon ratio of 4:1) reached 2088 m(2)/g and 1.240 cm(3)/g, respectively. The adsorption isotherms of N-2, CH4, and CO2 on five samples were determined by a volumetric method to obtain insight into the relationship between adsorption performance and porosity. CSK-5 with a developed pore structure exhibited a higher adsorption amount of CO2 and CH4 at high pressure. For the selectivity, the CS sample presented the highest selectivity for CO2/CH4, of which the selectivity of separation reached as high as 5.86. The highest selectivity of separation of CH4/N-2 (3.644) was present on CSK-7.