Li4 Ti5 O12 nanoparticles (LTO NPs) with different particle sizes were synthesized by a simple sol-gel progress. The effect of LTO particle size on the electrochemical behavior in Mg secondary batteries was investigated. Results showed that magnesium storage behaviors in LTO are strongly size dependent. The Mg(2+) electrochemical insertion into LTO becomes notable only when the particle size is below 40 nm. Moreover, the theoretical maximum capacity of LTO can be reached in crystallite sizes less than 10 nm. LTO NPs with 7-8 nm in size exhibited a substantial reversible capacity of 175 mA h g(-1) and outstanding cycling stability, maintaining 95 % capacity retention after 500 cycles. This result indicates that the LTO NPs with average particle size of 7-8 nm have high potential for use in high-rate and durable Mg secondary batteries. These results provide insight into how confining particles to nanosize will be critical to the preparation of suitable electrode materials for Mg secondary batteries.