The first several hundred atomic layers of anodized niobium were studied using ion scattering spectrometer analysis alternated with ion milling. The results show excess oxygen at the surface followed by a layer of stoichiometric Nb2O5. Below this was an unexpected ∼ 80-Å layer of NbO and, finally, the bulk metal, with oxygen in solid solution. These results have important consequences for some ac superconducting applications since NbO is a normal metal above 1.38 K.