The cycling stability of spinel LiMn2O4 with different particle sizes, varying from nano to micrometer scales, was studied in aqueous electrolyte at both room-temperature (25°C) and elevated temperature (60°C). The electrochemical test results indicate that LiMn2O4 exhibits almost same good cycling stability and rate capability at room temperature despite of the particle size, while it shows significant difference at the elevated temperature: LiMn2O4 with large particle size shows much better cycling stability with a capacity retention rate of 93% after 50 cycles, while the sample with smaller particle size shows poorer cycling stability with a capacity retention rate of 78%. Mn dissolution and thus leading to the electrode polarization which is mainly responsible for the capacity fading during cycling.