Preparation of LiFeO2–Li2MnO3 solid solution has been attempted using hydrothermal and solid state reactions. Three 10% Fe-doped Li2MnO3 samples (Fe/(Fe+Mn)=0.1) with different average particle sizes could be obtained by both methods. The initial charge capacities for these cathodes were sensitive to the preparation method; the capacity up to 4.3V is 45mAh/g for the hydrothermally-obtained sample, 24mAh/g for the post-annealed sample after hydrothermal-treatment at 673K, and 6mAh/g for the sample obtained by solid state reaction at 1173K. 57 Fe Mössbauer spectra detect the oxidation of Fe3+ to Fe4+/reduction of Fe4+ to Fe3+ after initial charging/discharging for the hydrothermally obtained sample. The observed Fe3+/4+ redox voltage is between 4.0 and 4.5V which is lower than that predicted (5V) for Fe-doped LiMn2O4. This suggests that hydrothermally synthesized Fe-doped Li2MnO3 is an environmentally–friendly candidate as cathode material, involving a Fe3+/4+ redox reaction for rechargeable lithium batteries.