PAN-based carbon fibers were stabilized under various tensions in the presence of air at 230°C and sequentially activated at 950°C following carbonization. The prepared carbon fibers were tested for their SO 2 adsorption capacity using a thermogravimeter. The magnitude of tension during stabilization and gas environment were varied to study their effects on SO 2 adsorption capacity. It was found that the tension during the stabilization and the gas atmosphere during activation affect the carbon fiber properties, which are closely related to the SO 2 adsorption capacity. The influence of stabilization tension and activation atmosphere on the SO 2 adsorption capacity appear to arise from their effects on the amount of oxygen functional groups and the surface area of carbon fiber. The highest SO 2 adsorption capacity and improved mechanical strength were observed when PAN fibers were activated under steam.