Without using inert gas to prevent the oxidation of Fe²⁺, Fe₃O₄ nanorods with diameters of about 30 nm have been successfully synthesized in a microwave-assisted ionic liquid method at 363 K for 10 min. The starting reagents were FeCl₃, FeCl₂.4H₂O, NaOH. Comparing to the traditional methods, the whole reaction process can be carried out more easily and quickly. Our result shows that temperature and time of microwave irradiation played important roles in the purity of Fe₃O₄ and the formation of Fe₃O₄ with different morphology_. Well-crystallized nanometer Fe₃O₄ could be synthesized in the presence of [bmim]BF₄ (1-buty-3-methylimidazolium tetrafluoroborate) under microwave irradiation or in oil bath. The products were characterized by X-ray powder diffraction (XRD) and transmission electron microscopy (TEM).