The catalytic behavior in propane ammoxidation to acrylonitrile of V-Sb-oxides prepared by four different methods and with a Sb : V ratio in the 0.8-3.0 range was studied and analyzed in relation to the structural/composition features of these samples determined by XRD, IR and SEM-EDX techniques. In particular, the following aspects are discussed : (i) composition, (ii) local homogeneity and morphology of the samples, () presence, amount and dimensions of crystalline phases, (iv) presence and nature of the amorphous phases, and (v) crystallographic and non-stoichiometric features of the approximate to VSbO4 phase. It is suggested that the selective behavior in propane ammoxidation is related principally to the nonstoichiometry of the approximate to VSbO4 phase and especially the creation of a Sb-rich approximate to VSbO4 phase, the formation of which depends on the microstructure of the catalyst, chemistry of preparation and Sb : V ratio.