Nano-sized γ-MnOOH (manganite) has been synthesized by a new route via the reduction of KMnO₄ with sucrose and MnSO₄ in acidic medium under refluxing conditions. Manganite has the highest activity in the electrocatalytic reduction of O₂ of many manganese oxides (e.g. Mn₂O₃, Mn₃O₄, and Mn₅O₈). Characterization of the synthesized manganite using XRD, FESEM, TEM, TGA, IR and CV was done. Particle sizes of up to 80 nm can be obtained when the reducing agents were added slowly together to KMnO₄. Smaller particles (up to 30 nm) can be obtained when the addition of MnSO₄ was added after sucrose was reacted with KMnO₄. When incorporated in Yardney's medium-sized lithium-air battery, the larger particles gave higher specific capacity (up to 2.2 Ah/g), which corresponds to 38% increase in specific energy of the battery when compared to a battery where no manganite was incorporated.