Nanosized lithium titanium oxide (Li4Ti5O12) powder has been prepared using LiCl as a high-temperature flux. X-ray diffraction, scanning electron microscope, and transmission electron microscope measurements indicate that the obtained Li4Ti5O12 particles are uniform and the particle size of Li4Ti5O12 powder can be controlled by flux content and heating time. Under the optimal synthetic condition, the particle- size distribution is narrow (similar to 100 nm). The hybrid electrochemical supercapacitors using a nanosized Li4Ti5O12 negative electrode in combination with an activated carbon positive electrode show much better rate capability than those based on the conventional Li4Ti5O12 prepared by solid- state reaction. (c) 2006 The Electrochemical Society.