VOx catalysts supported on SBA-15 with and without MgO modification were prepared and characterized by N-2 adsorption-desorption, XRD, HRTEM, H-2-TPR, NH3-TPD and XPS. Compared to the VOx/SBA-15 catalyst, the VOx/MgO/SBA-15 ones exhibit much higher C-4-olefins selectivity and yield in the oxidative dehydrogenation of n-butane. The enhanced performance can be attributed to the rise in VOx reducibility as well as to the relatively lower acidity of the MgO-modified SBA-15 materials. (C) 2007 Elsevier B.V. All rights reserved.