The availability of high-quality nanocrystals underpins a diverse range of applications and investigations into size-dependent physical and chemical properties. Effective synthetic methods that yield uniform nanocrystals are critically important. Here we demonstrate a fast and economical microwave-assisted solid-state method to prepare spinel Li4Ti5O12 nanocrystallites in large quantities using cost-effective commercial TiO2 as a raw material of titanium. This method easily programs the synthetic conditions including temperature and time, and significantly shortens the synthesis time to minutes. The morphology and microstructure of the products were characterized by X-ray diffraction, scanning electron microscopy, transmission electron microscopy, and Raman spectroscopy. When evaluated as an anode material for lithium-ion batteries, the as-formed Li4Ti5O12 nanocrystals prepared by microwave irradiation exhibit greatly enhanced electrochemical lithium-storage performances, including not only high rate capabilities but also a highly reversible capability of ∼160mAhg−1 over 500 cycles at 1C.