Abstract: VOx/MgAl2O4 catalysts with different V2O5 loadings were prepared by the incipient wetness impregnation and their isobutane dehydrogenation activities were investigated. X-ray diffraction (XRD), nitrogen adsorption-desorption, Fourier transform infrared (FT-IR) spectroscopy and hydrogen-temperature programmed reduction (H2-TPR) were used to characterize the structure and reducibility of vanadium species on the surface of MgAl2O4. The results show that the isolated and polymeric VO4 species on the surface are present at low vanadium loading of <5% and can be reduced more easily than samples with higher vanadium loading. With increase of V2O5 loadings, mixed magnesium vanadate compounds (Mg3V2O8, Mg2V2O7) appear, which are difficult to reduce by hydrogen. At the optimum V2O5 loading (5%), yield of isobutylene was 31.4% with the corresponding isobutane conversion of about 41.9% at 560 ℃，reaction time 1.5h. Based on the experimental results, it is suggested that low valence Vδ+ (δ<5) species on the surface are the active sites for this reaction..