Abstract: Pretreatments of the viscose rayon based activated carbon fibers (ACFs) with acid (HNO3, H2SO4, HCl), alkali (NaOH) and steam were carried out to modify the surface characters of ACFs. The activities of ACFs for selective catalytic reduction (SCR) at lower temperature were tested. There is an increase in the content of functional group with oxygen on the surface of ACF and a decrease in micropore range for the ACF treated with HNO3. The new functional groups are formed for the ACF treated with H2SO4, HCl and NaOH, which can improve the activity of SCR, and an increase in micropore range for ACF treated with NaOH is found. However, the portion of mesopores increases but the catalytic activity of ACF decreases for the ACF treated with steam.