The valence of Fe is important not only for chemical properties but also for magnetism and catalytic activity and so on. Fe substituted Li2MnO3 is known as a novel positive electrode material for high-capacity Li-ion battery. In the study of this material, high-valent (4+ or over) Fe ions were observed. In the previous studies, most of such high-valent Fe ions had been observed in the octahedral site of perovskite structure, for example, SrFeO3. However, Li2MnO3 has a rock-salt related structure. To elucidate the origin of this high-valent Fe, we observed 57Fe Mössbauer spectroscopy of Li1 + x(Fe0.2Mn0.8)1-xO2. The Mössbauer spectra measured at 3 K contained magnetic Fe4+ and Fe5+. The area ratios of these components in the sample calcined in oxide were larger than those in the sample calcined in nitrogen. This result did not agree with the ratio of Fe sites obtained from X-ray diffraction. These high iron oxides are thought to be expressed by interaction with oxygen rather than site differences.