High-purity Fe3S4 (greigite) microcrystals with octahedral shape were synthesized via a simple hydrothermal method using a surfactant. The as-prepared samples have the inverse spinel structure with high crystallinity. The saturation magnetization (M-s) reaches 3.74 mu(B) at 5 K and 3.51 mu(B) at room temperature, which is larger than all reported values thus far. Electrical transport measurements show metallic behavior with a resistivity 40 times lower than in an previous report, The potential use of greigite as an anode in lithium-ion batteries was investigated by cyclic voltammery and galvanostatic discharge-charge cycling On as-prepared samples. The discharge capacity was 1161 mAh/g in the first cycle and 563 mAh/g in the 100th cycle. This excellent electrochemical performance can be attributed to the high purity, crystallinity, and favorable morphology of the products.