Hydrotalcite-like compounds containing (a) Mg^II, Al^III and V^III in the layers and carbonate in the interlayers, or (b) Mg^II and Al^III in the layers and decavanadate in the interlayers, have been synthesized and characterized using powder X-ray diffraction, thermal analysis, FTIR spectroscopy. temperature-programmed reduction, and specific surface-area determination. The crystalline phases formed after calcination in air at 700 °C have been identified using these same experimental techniques. It has been found that the nature of the precursor determines the nature of the Mg–V–O phases formed; thus, when starting from (a), Mg₃(VO₄)₂ containing isolated [VO₄] units is formed, while when starting from (b), MgV₂O₆, containing pairs of edge-sharing [VO₆] octahedra, is formed preferentially. Such a reactivity appears to depend on the nature of the support, and not on the stoichiometry (i.e., Mg/V atomic ratio) of the starting materials.