The one-step oxydehydration of glycerol to acrylic acid over molybdenum and vanadium mixed oxides was investigated. The Mo-V oxide catalysts were prepared by a simple hydrothermal method under different synthesis and calcination atmospheres and were characterized by in situ XRD, TPD-NH3, N-2 adsorption/desorption, X-ray absorption near vanadium K-edge spectroscopy and thermogravimetry. The catalytic performance of the samples at different temperatures (290, 320 and 350 degrees C) and under different gas flow compositions (20% O-2 in N-2, 100% O-2, or 100% N-2) revealed that the arrangement of the crystallographic structures of the active phases directly influenced the catalytic performance. It was found that the catalysts heat-treated in oxidizing atmosphere gave superior catalytic results comparing with the catalysts heat-treated in inert atmosphere due to the equilibrium between the crystalline phases MoVO5 and Mo4.65V0.35O14 that contains V+4 and V+5. Catalytic oxydehydration at 320 degrees C under a flow of 100% O-2 gave the best performance, achieving selectivity of 33.5% towards acrylic acid and 100% conversion of glycerol.