Here we employ both Fe K and L2,3 edge X-ray absorption near-edge structure (XANES) spectroscopy techniques to clarify that in the B-site ordered double-perovskite halfmetal, Sr2FeMoO6.0, iron possesses a mixed-valence state, FeII/III, and accordingly, molybdenum a mixed MoV/VI valence state. A reliable interpretation of the spectral features has been made possible by using a series of samples of the Sr2Fe(Mo, W/Ta)O6.0 system. Replacing Mo V/VI gradually with WVI causes an increasing amount of Fe to adopt the FeII state, whereas TaV substitution shifts the valence of iron toward FeIII. As the valence of Fe increases from II to III in the Sr2Fe(Mo, W/Ta)O6.0 system, the absorption energy at the Fe K-edge gradually shifts toward the higher energy side. Similarly, in the L2,3-edge XANES spectra intermediate spectral features are revealed for the Sr2FeMoO6.0 sample in comparison with those for samples heavily substituted with either W or Ta.