A mild hydrothermal method has been developed to synthesize spinel-type lithium manganese oxide nanocrystallites directly from commercial LiOH, Mn(NO3)(2) and H2O2 at 90-110 degreesC for 8 h. The as-prepared products were characterized by X-ray diffraction (XRD), inductively coupled plasma-atomic emission spectroscopy and chemical analysis. The analysis results indicated that spinel-type lithium manganese oxides with the compositions of Li1 + xMn2 - xO4 - delta (0.09 less than or equal to x less than or equal to 0.28, delta < 0.05) could be obtained by varying the synthesis parameters, such as the concentration of LiOH solution used. Transmission electron microscopy (TEM) images showed that the obtained spinet at 110 degreesC was cubic-shaped with the average size of around 40-50 run. Finally, the thermal behaviors of the obtained lithium-rich spinel Li1.28Mn1.72O3.99 were investigated by thermogravimetric analysis (TG) and differential thermal analysis (DTA).