Vanadium and mixed vanadium and iron antimonates with rutile-type structures have been studied by XANES at Sb L-1 edge, Fe-57 Mossbauer spectroscopy and ESR spectroscopy at 77 K. The results showed that both antimony and iron remained at their highest oxidation state, i.e. Sb-V and Fe-III, whereas vanadium was present as V-III and V-IV. Two types of V-IV species were distinguished corresponding to well-isolated vanadyl species in distorted octahedral coordination and vanadyl species in the same coordination but close to each other and in a dipole-dipole interaction. Both V-III and total V-IV concentrations decreased when the iron content increased, whereas isolated V-IV concentration increased first and then decreased, with a maximum for x = 0.2 in FexV1-xSbO4. The observed variations in cationic composition are discussed in relation with the catalytic properties of the compounds in the ammoxidation of propane. Isolated V-IV-O moieties appeared to be the most active and selective catalytic sites.