Two phases have been investigated in the MgOVO 2 system at 900°C. MgVO 3 crystallizes in the orthorhombic system, space group Cmc2 1, with a = 5.243 Å, b = 10.028 Å, and c = 5.290 Å. The structure is built up from square pyramids VO 5 and MgO 5 sharing edges and forming sheets connected through oxygen atoms. Its structure is related to the ReO 3 and Mg 2NF structures. MgV 2O 5 is orthorhombic with a = 3.696 Å, b = 9.965 Å, and c = 11.019Å; the space group is Cmc2 1, Cmcm, or C2 cm. Our structural data for MgVO 3 do not agree with the ones published by Cros, Tourne and Philippot ( 16).