Vanadium- and magnesium-containing aluminophosphates with AFI structure (MgVAPO-5) have been prepared by hydrothermal synthesis using triethylamine as template. XRD patterns of AFI structure were observed on both as-synthesized and calcined materials, although their crystallinities depend on the preparation conditions. FTIR of pyridine adsorbed and TPD of NH, indicate the presence of acid sites, related to the incorporation of Mg2+ cations into the framework of AFI structure. However, EDX and SEM results indicate a different incorporation of vanadium and magnesium depending on the crystal size. These results indicate some heterogeneity of Mg- and/or V-containing materials. MgVAPO-5 catalysts are active and selective in the oxidative dehydrogenation of ethane. Isolated vanadium species are the active sites while the selectivity to ethene is also related to the presence of acid sites.