Mo-V-Te-Nb-O catalysts have been prepared by hydrothermal synthesis and have been tested in the selective oxidation of propane to acrylic acid. The catalysts have been prepared by using different Te- and Mo-starting compounds. Both the catalyst characterization results (XRD, SEM-EDX, FTIR and XPS) and the catalytic tests show important differences depending on the Te- and Mo-starting compounds used in the hydrothermal synthesis. The most active and selective catalysts for the oxidation of propane to acrylic acid were those prepared from Te(VI)-compounds, i.e. telluric acid or an Anderson-type telluromolybdate. However, catalysts prepared from Te(IV) -compounds, i.e. TeO2 or (NH4)(4)TeMo6O22.2H(2)O, presented both low activity and low selectivity to acrylic acid. In the best catalysts, several crystalline phases were observed: Mo5TeO16, (Mo0.93V0.07)(5)O-14, and/or Nb0.09Mo0.91O2.80 and new Te-V-Nb-Mo-oxide crystalline phases. The presence of small crystals of MoO3 in active and selective catalysts can also be proposed. The different catalytic performance of these catalysts could be related to the different incorporation of Te, V and Nb ions, which depends strongly on the Te-compound introduced in the synthesis gel. (C) 2003 Elsevier Science B.V. All rights reserved.