Bi1-xYxO1.5+delta (x similar to 0.4, 0 < delta < 0.16) is a recently identified bismuth mixed-valence oxide. To provide clear evidence of the valence state of the Bi ion, Bi L-3 X-ray absorption near edge structure (XANES) spectra were measured in polycrystalline materials. These spectra were found to be similar to that of Bi2O3 as a reference to B3+. An observed systematic decrease centered on similar to 13427 eV associated with the increase of delta was clarified by subtracting the spectrum of delta = 0 from that of delta = delta. The spectrum of delta = 0.5, which was calculated using both delta = 0 and delta = 0.16, was similar to that of NaBiO3. As delta increased, the position of the inflection point of the main peak at about 13448 eV, assigned to a 2p-6d transition, shifted toward higher energy. This indicated the oxidation of Bi ions in Bb(0.6)Y(0.4)O(1.5+delta).