Abstract: Macroporous Rayon-based activated carbon fibers (ACFs) were produced from Rayon precursors impregnated with alkali metal salt and Lewis acid followed by chemical activation or water vapor activation. The effect of pretreatment conditions such as the concentration of alkali metal salt and impregnation time on the properties of the resultant ACFs were investigated by scanning electron microscopy and physical adsorption. Results showed that the pore sizes and their distribution could be controlled by the concentration and impregnation time of the alkali metal salt. A novel ACF with abundant macropores and micropores and with high specific surface area was obtained by an optimum pretreatment with alkali metal salt.