The solid state synthesis of the phase“Ce3NbO7+δ”, from stoichiometric quantities of CeO2 and Nb2O5, was investigated under air atmosphere, as previously described by Zhang et al. (Journal of Rare Earths, 2007, 25, 730-733). A combination of powder X-ray diffraction, scanning electron microscopy with energy dispersive X-ray analysis, and laboratory Ce L3 X-ray absorption spectroscopy, demonstrates the product of the reaction to be a mixture of CeO2 and CeNbO4. These data, and reexamination of the published X-ray diffraction data of“Ce3NbO7+δ”, are consistent with this phase in fact being CeO2. No evidence for the formation of a phase of composition“Ce3NbO7+δ”is found, by solid state synthesis under air atmosphere.