To determine the role of sulfur groups formed on activated carbon (AC) in the selective catalytic reduction (SCR) of NO with NH3, coal-based AC was modified by H2SO4 under various conditions and then treated in N2 atmosphere at 400 oC. The resulting carbons were characterized by N2 adsorption, elemental analysis, temperature programmed desorption and X-ray photoelectron spectroscopy, and tested for the SCR of NO with NH3 in the temperature range of 30-250 oC. Results reveal that H2SO4 modification has little effect on the textural properties, but promotes the formation of sulfur and oxygen groups. The sulfur groups incorporated by H2SO4 modification are mainly sulfonic groups and then sulfates. In particular, these sulfur groups play a predominant role in improving NH3 adsorption and then enhancing the SCR activity of modified carbons above 150 oC. However, the contribution of oxygen groups to NO reduction is very limited under the conditions employed in this work.