Catalytic activity of a series of pitch-based activated carbon fibers (ACFs) was examined at room temperature for the oxidative removal of SO2 as aqueous H2SO4 which was continuously recovered at steady state. Calcination up to 900 degrees C in an inert atmosphere increased the activity very markedly regardless of the ACF; however, higher temperatures up to 1200 degrees C increased the activity of ACFs with larger surface area (1000 m(2)/g) while the ACFs with smaller surface area lost activity very sharply. ACF with the largest surface area and calcined at 1100 degrees C resulted in the complete capture of 1000 ppm SO2 by ACF weigh/flow rate (W/F) 1 x 10(-3) g . min/mL under 10% H2O. Lower humidity reduced the activity, although larger W/F allowed complete removal of SO2. TPDE measurements revealed CO evolution from the ACF in the range of 400-1100 degrees C, the amount and the range depending on the ACF. ACF with the highest activity appeared to be obtained when the major CC-evolving groups were removed before marked reduction of the surface area took place. ACF that evolved CO more exhibited higher activity. The active site produced by CO evolution is discussed briefly.