Oxidative fixation of SO2 into aqueous H2SO4 was examined at 50-70 degrees C over a pitch-based active carbon fiber (ACF) of large surface area. A higher temperature was found to require higher humidity and a longer contact time for the complete removal of SO2 at the stationary state. Smaller adsorption of SO2 and less condensed water on the ACF make it difficult to fix SO2 on the ACF and to elute aqueous H2SO4 continuously from the ACF, as revealed by the adsorbed SO2 on ACF and the eluted aqueous H2SO4 from the bed. Among the ACFs of different calcination temperatures, a particular ACF of the largest surface area calcined at 1100 degrees C showed the largest activity regardless of the reaction temperatures and humidity, indicating a major influence of the number of active sites. The hydrophilicity of the ACF has little influence on condensing water on the ACF above room temperature.