Effect of carbon dioxide on the reaction performance of oxidative dehydrogenation of n-butane over vanadium-magnesium-oxides (V-Mg-O) catalyst was investigated using a conventional fixed-bed reactor. The catalyst characterization was carried out by XRD, TPD, TPR and BET technology. With the CO 7 partial pressure in the feed increases, the n-butane conversion decreases slightly but the selectivity and yield to C-4 dehydrogenation products increase. The selectivity to C4 dehydrogenation products of up to 70.2% and yield of 34.1% were obtained by adding proper amount of CO2 in the feed at 873 K. The high catalytic performance may be due to the competition between molecular O-2 and CO2 adsorption on the active sites that are responsible for deep oxidation. (C) 2003 Elsevier Science B.V.. All rights reserved.