Nanosized and highly crystalline spinel lithium titanium oxide (Li4Ti5O12, LTO) particles are synthesized in supercritical water. The effects of various synthesis conditions – feed concentration, reaction time, and calcination – on the particle properties, including particle size, surface area, particle morphology, phase purity, and crystallinity, are carefully analyzed. Phase-pure LTO particles are obtained with a long reaction time of 6h in supercritical water at 400°C and 300bar without subsequent calcination, while the anatase TiO2 impurity phase is detected at shorter reaction times of 5min to 2h. Particles synthesize in supercritical water with subsequent calcination at a relatively low temperature of 700°C exhibit the highly crystalline LTO phase. Based on the analytical results using scanning electron microscopy (SEM), high-resolution transmission electron microscopy (HR-TEM), and X-ray diffraction (XRD), an LTO formation mechanism in supercritical water is proposed. LTO particles prepare in supercritical water with subsequent calcination exhibit excellent long-term cyclability and high-rate performance. The discharge capacity after 400 cycles at 1C is 117.2mAhg−1, which is approximately 80% of the initial discharge capacity (147.1mAhg−1), and the discharge capacity at 10C is 100.5mAhg−1. These electrochemical performances are significantly better than those of uncalcinated LTO synthesize in supercritical water and solid-state synthesize LTO.