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.