Abstract: A series of activated carbon fibers (ACFs) was prepared by carbonizing pre-oxidized PAN fibers at temperatures ranging from 400 to 900℃ followed by CO2 activation and the effect of carbonization temperature on the porous structure of polyarcylonitrile (PAN)-based ACFs characterized by nitrogen adsorption was investigated. It is found that the porous structure of PAN-ACF depends strongly on the carbonization temperature, and a moderate carbonization temperature (600℃) is favorable to obtain ACFs with higher specific surface area, larger pore volume and larger pore size.