Nb-free (SbO)(2)M20O56 catalysts (M = Mo, V) presenting pure M1 phase have been prepared by a post-synthesis treatment with hydrogen peroxide of a heat-treated MoVSbO mixed metal oxide catalyst previously prepared by hydrothermal method. The characterization of catalysts and their results for propane oxidation suggest that the optimization in the preparation of the M1 phase depends strongly on the washing procedure. The optimal removing of Sb species formed during post-synthesis treatment can explain the improvement in the catalytic activity; while the better selectivity to acrylic acid of the catalysts obtained by post-synthesis treatment can be explained by the elimination of M2 phase and the modification of the M1 phase crystals surface. The importance of M1 phase in the catalytic performance during the selective propane oxidation over Nb-free Mo-V-Sb based catalysts is also discussed. (C) 2008 Elsevier Inc. All rights reserved.