Highly crystalline nano-sized lithium manganese oxide particles were fabricated by spray pyrolysis. The resultant particles had well-developed facet planes in a transmission electron microscopy (TEM) image and electron diffraction pattern from a single particle also showed clear diffraction spots, indicating that the prepared particles were highly crystalline. The mean crystallite size estimated from X-ray diffraction peaks was ca. 18nm, which was in good agreement with the diameter of the particles observed in the TEM image. These particles were gathered on platinum mesh and their electrochemical properties were investigated. The mean crystallite size increased with an increase in annealing temperature, which influenced the electrochemical lithium insertion/extraction properties of the particles. In particular, samples annealed at 773K showed different kinds of lithium extraction/insertion properties in the cyclic voltammogram (CV), and only a couple of broad redox peaks were observed at around 0.8V (versus Ag/AgCl) between 0.4 and 1.0V. It is suggested that lithium distribute randomly in the sample annealed at 773K sample due to the effects of grain boundaries, which resulted in different kinds of phase transition reactions.