Vanadium-magnesium oxide (VMgO) catalysts with vanadium loadings of 15 and 20 wt% were prepared by the method of wet impregnation. The prepared catalyst were characterized by IR and Raman spectroscopy, Powder XRD, ICP-OES, N-2 adsorption desorption isotherms, oxygen chemisorption, TPR, TPD, SEM, SEM-EDX and TEM. From XRD and IR analyses, vanadium was found to be present in two phases i. e. orthovanadate and pyrovanadate. Dispersion of vanadium on the MgO was in the range of 30-40 % and oxygen chemisorption capacity increased with the vanadium loading. The catalysts were tested in a continuous flow fixed bed reactor at a GHSV of 4,000 h(-1) over a temperature range of 350-550 degrees C at an nheptane to oxygen molar ratio of 1:1. Oxidative dehydrogenation of n-heptane showed that product selectivity depends on the phase of vanadium present on the MgO catalysts and conversion is proportional to the amount of chemisorbed oxygen on the surface of the catalyst. Carbon oxides are the major products over the MgO support, whereas heptene isomers are the major products over the VMgO catalysts. 2-Heptene, toluene and 2-heptanol are the dominant products in the heptene isomers, aromatics and oxygenate products respectively.