The structure of uranyl ion in 1-butyl-3-methylimidazolium nonafluorobutanesulfonate ionic liquid (BMINfO) has been studied with iN-and 35C1-NM~ Raman, and UV-visible spectroscopy. In the ~H-NMR spectrum of the BMINfO solution prepared by dissolving UO2(CIO4)2-5.6HzO, the signal of H20 coordinated to UO22รท was observed at 6.64 ppm at 50ยฐC (free HzO in BMINfO: -3.1 ppm at 50ยฐC), suggesting that the uranyl species exists as the aquo complex, [UO2(H20),] 2+. The signal of the coordinated H20 disappears with heating at 120ยฐC for 3 h under vacuum. This indicates the dehydration from [UO2(H20)n] 2+. On the other hand, the 35C1-NMR signal of C104 as the counter anion of UO22+ was observed at 1011 ppm (vs. CI-in D20) regardless of heating. This indicates that no CIO4 ion is in the first coordination sphere of UO22+. Furthermore, the UV-visible absorption spectra showed that the characteristic absorption bands due to UO22+ were sharpened with the dehydration. This means the simplification of the structure around UO2 z+. These results described above suggest that UO22+ in BMINfO has no ligand in its equatorial plane after the dehydration, i.e. UO22+ exists as a bare cation in this system.