The oxidation state of vanadium cations in nanosized vanadium-iron spinels at stoichiometry and at oxidative nonstoichiometry has been investigated by associating X-ray diffraction, thermal analysis (DSC), infrared and X-ray photoelectron spectroscopies. it has been established that, during oxidation, the V3+ cations present several intermediate valencies before to realize the final oxidation state +5. A comparison was made with the oxidation of V2O3.