Alumina-supported V0.43Sb0.57 oxide (VSb/Al) and MgO-modified alumina-supported V0.43Sb0.57 oxide catalysts (VSb/MgnAl with Mg/Al atomic ratio, n = 0.1, 0.3 or 0.5) have been tested for the dehydrogenation of ethylbenzene with carbon dioxide as an oxidant. Their catalytic behaviors were interpreted by results of several catalyst characterization methods. The decrease in the surface acidity of the VSb/MgnAl catalysts due to modification of alumina with MgO favors the prolonged time-on-stream activities. However, the addition of relatively large amounts of MgO (n = 0.3 or 0.5) causes substantial decrease in their surface areas, reducibility of active vanadium oxide component and, consequently, ethylbenzene conversion. These negative factors did not become apparent for the most efficient VSb/Mg-0.1 Al system demonstrating high and stable catalytic activity. (c) 2007 Published by Elsevier B.V.