Abstract The oxidative dehydrogenation of ethylbenzene to styrene was studied on single-phase magnesium vanadates Mg 2VO 4, Mg 3(VO 4) 2, Mg 2V 2O 7 and MgV 2O 6. Both the V V Mg 3(VO 4) 2 and the V IV Mg 2VO 4 were found to be active and selective, while MgV 2O 6 and Mg 2V 2O 7 showed low styrene selectivities. The V V Mg 3(VO 4) 2 and the V IV Mg 2VO 4 shared similarities in structure and underwent partial phase interconversion via reduction and oxidation. The V V Mg 3(VO 4) 2 was stable under the flow reaction conditions, giving a rather constant styrene selectivity of about 80% between 450 and 525°C. However, the styrene selectivity was decreased by increasing the O 2/ethylbenzene ratio in the feed. Adding steam to the feed increased the styrene selectivity slightly. The V IV Mg 2VO 4 was gradually oxidized under the flow reaction conditions. Also studied were the reducibilities of these vanadates. It was found that the reducibility of an oxide as measured by H 2-TPR could be very different from that deduced from its reaction with hydrocarbon. The nature of the lattice oxygen and its interaction with different reductants are discussed to explain the difference in reducibility as well as in catalytic characteristics between the four magnesium vanadates.