In recent years, various studies have been reported on decomposition of carbon dioxide into carbon using iron oxide. This study investigates the ability of mechanically-milled magnetite powder to decompose carbon dioxide as well as the effect of mechanical milling on the crystal structure change. Mechanical milling was performed on magnetite powder using a high-energy vibration ball-milling machine. After 6-12h of milling, Fe and alpha Fe2O3 phases appear in addition to the magnetite phase, followed by disappearance of the alpha Fe2O3 phase after 24 h of milling, and an FeO phase appears after 72-168 h. The Fe3O4 content phase gradually decreases with milling. The carbon dioxide decomposition with the milled powder was carried out in a quartz tube for 3 h at 773 K. The carbon content of the sample after the CO, decomposition increases slightly with the milling time up to 48 h and shows drastic increase when the milling time is longer than 72 h, indicating that the production of FeO phase contributes to the ability of CO, decomposition. After the decomposition the sample contains graphite (or other types of carbon), undissolved Fe (both bee and fee structure) and Fe3O4 phase. (C) 2006 Elsevier B.V. All rights reserved.