Li1−y Ni1/3Mn1/3Co1/3O2 (y =0–0.7) was characterized using neutron diffraction and X-ray absorption fine structure (XAFS) measurements. LiNi1/3Mn1/3Co1/3O2 adopted the α-NaFeO2 structure and was demonstrated that the chemical formula can be expressed as [Li0.97Ni0.03]3a[Li0.03Ni0.30Mn0.33Co0.33]3bO2. The Li/Li1−y Ni1/3Mn1/3Co1/3O2 cell showed a discharge capacity of 160mAhg−1 in the voltage range 4.6–2.5V. The Ni K and LII,III-edge X-ray absorption near edge structure (XANES) results clarified the contribution of the Ni ion to charge compensation up to y =0.7 and the rehybridization of the Ni 3d orbital with O 2p orbital above y =0.5. The Co K-edge extended X-ray absorption fine structure (EXAFS) results clarified that the CoO bond lengths decreased up to y =0.7 with Li de-intercalation, while the Mn K-edge EXAFS results indicated that the MnO bond lengths showed essentially no change over the whole composition range. These results supported that the Li de-intercalation from LiNi1/3Mn1/3Co1/3O2 proceeded mainly by the valence state change of Ni and Co ions over the whole composition range. The combination of XAFS analysis using hard and soft X-ray data is a powerful method in clarifying the mechanism of the Li de-intercalation process in this system.