Gamma-Al2O3 and TiO2 supported 20 wt.-% MgVO catalysts with Mg/V atomic ratio varying from 1/1 to 4/1 were investigated for the oxidative dehydrogenation of propane. The selectivity increases but activity decreases with the increase of Mg/V atomic ratio. In-situ laser Raman spectra showed that the MgVO species formed on the supports are mainly magnesium pyrovanadate and/or orthovanadate. Moreover, highly dispersed monomeric vanadyls were also observed to be present on (1/1) MgVO/TiO2 and on all the gamma-Al2O3 supported-MgVO catalysts. Correlation of the structure and reaction data indicates that the nature of the support controls the MgVO species formed on the surface, and the catalytic performance for the oxidative dehydrogenation of propane is primarily determined by the concentration of vanadium oxide and the Mg/V atomic ratio of the catalyst.