Fe-substituted Li2MnO3 including a monoclinic layered rock-salt structure (C2/m), (Li1+x (Fe y Mn1−y )1−x O2, 0< x <1/3, 0.1≤ y ≤0.5) was prepared by coprecipitation–hydrothermal–calcination method. The sample was assigned as two-phase composite structure consisting of the cubic rock-salt ( F m 3 ¯ m ) and monoclinic ones at high Fe content above 30% (y ≥0.3), while the sample was assigned as a monoclinic phase (C2/m) at low Fe content less than 20%. In the monoclinic Li2MnO3-type structure, the Fe ion tends to substitute a Li (2b) site, which corresponds to a center position of Mn4+ hexagonal network in Mn–Li layer. The electrochemical properties including discharge characteristics under high current density (<3600mAg−1 at 30°C) and low temperature (<−20°C at 40mAg−1) were severely affected by chemical composition (Fe content and Li/(Fe+Mn) ratio), crystal structure (monoclinic phase content) and powder property (specific surface area). Under the optimized Fe content (0.2< y <0.4), the Li/sample cells showed high initial discharge capacity (240–300mAhg−1) and energy density (700–950mWhg−1) between 1.5 and 4.8V under moderate current density, 40mAg−1 at 30°C. Results suggest that Fe-substituted Li2MnO3 would be a non-excludable 3V positive electrode material.