Abstract: The surface chemical structure of activated carbon fibers (ACF) was modified by cerous nitrate. The pore structure and surface chemical structure were characterized by nitrogen adsorption, Xray photoelectron spectroscopy (XPS) and thermal gravimetric analysisFourier transformation infrared integrated technology. Results show that Ce(IV)treatment can result in about a 1020% decrease of specific surface area of the modified ACF, however this treatment cannot obviously change the micropore size distribution. Surface chemical structure analysis based on XPS indicates that Ce(IV)treatment can evidently increase the oxygen content of ACF from 11 to 25 atom% depending on the concentration of cerous nitrate. In situ IR analysis of the decomposition gases from ACF during heating to high temperature shows that the chemical treatment of ACF with a higher concentration of cerous nitrate can form many oxygencontaining groups such as carboxyl or lactone groups on the modified ACF, which is consistent with the results based on XPS.