The Li-Mn-spinel was synthesized using hydrothermal reaction through gamma -MnOOH in 0.050 similar to 0.150 mol/l LiOH aqueous solution at 130 similar to 170 degreesC. The composition of the as-precipitated Li-Mn-spinel depended on both the reaction temperature and the concentration of LiOH aqueous solution. The particle was rod-shaped and the average size was around 0.2 x 0.2 X 1 mum The charge-discharge characteristics of the as-precipitated Li-Mn-spinel were investigated in the system of Li-Mn-spinel/EC-DEC/Li. The as-precipitated Li-Mn-spinels showed an electrochemical behavior comparable to those prepared using the conventional calcination method, and the first discharge capacity varied from 62 to 107 mAh/g depending on Li content in the spinel.