In this study, vanadium-magnesium oxide (VMgO) catalysts with different vanadium loadings were synthesized by the impregnation method and characterized by BET, ICP-OES, IR, powder XRD, TEM, SEM, TPR-H-2, and TPD of ammonia. The catalysts were tested for the oxidative dehydrogenation (ODH) of n-octane in a continuous flow fixed bed reactor at GHSV of 6000 h(-1) and a temperature range of 350-550 degrees C using air as an oxidant and nitrogen as a make-up gas to give 9% n-octane in the gaseous mixture. The results showed that the vanadium concentration affects both textural and chemical properties of the catalysts and consequently their catalytic activity and selectivity towards the desired products (octenes and aromatics). The catalyst with a V2O5 concentration of 15% showed the best catalytic activity and productivity for the ODH products; especially for 1-octene and styrene. (C) 2009 Elsevier B.V. All rights reserved.