Magnesium oxide/hydroxide was deposited on pitch-based activated carbon fibers which were previously oxidized in air at different temperatures, and the changes in carbon oxidation activity, microporosity, and CH4 adsorptivity of the parent carbons due to Mg deposition were examined. DTA results, chemical analysis, and DRIFT spectra indicate that Mg species are mainly supported on the -COOH groups of the parent carbons, which serve as the catalysts to improve the oxidation activity of carbon. Mg deposition either increases or decreases the specific surface area, pore volume, and average micropore width of the parent carbon depending on the preoxidation temperatures. Mg deposition does not simply enhance CH4 adsorptivity: the complex changes are due to the differences in the supporting states of Mg species and slight modifications in micropore structure. (C) 2004 Elsevier Inc. All rights reserved.