Activated carbon fibers (ACFs) were prepared by CO2 activation of chars obtained by pyrolyzing Nomex [poly (m-phenylene isophthalamide)], either alone or pre-impregnated with phosphoric acid (impregnation ratio of 7 wt.% H3PO4). The resulting materials were characterized by elemental analysis, X-ray diffraction, SEM-EDX, thermogravimetry and N-2 (77 K) and CO2 (273 K) adsorption. Nomex impregnation with phosphoric acid produced an increase in the char yield in pyrolysis (64.1 vs. 53 wt.% without impregnation) and enhanced the reactivity during activation by an almost sevenfold factor. ACFs with BET surface areas as high as 1300 m(2) g(-1) at bum-off degrees of the order of 40% are obtained from both nonimpregnated and impregnated Nomex. (C) 2002 Elsevier Science B.V. All rights reserved.