Fe 3 O 4 nanosheets were successfully synthesized via a facile sonochemical route by direct ultrsound treatment of the mixture solution of FeSO 4 , NaOAc, and NaOH in the air. The results of X-ray diffraction (XRD), infrared spectra (IR), and X-ray photoelectron spectroscopy (XPS) showed that a purity phase of Fe 3 O 4 was obtained after sonochemical reaction. And results from transmission electron microscopy (TEM) indicated that the as-prepared Fe 3 O 4 nanosheets display single-crystalline structure with a lateral size altering from 50 to 120nm and a thickness ranging from 10 to 20nm, which was also confirmed by selected area electron diffraction (SAED) and HRTEM (high resolution TEM) analysis. In addition, magnetic measurements showed that the saturated magnetization of the obtained Fe 3 O 4 nanosheets was ferromagnetic property at room temperature. It was found that the sonochemical process played a key role in the formation of Fe 3 O 4 nanosheets and a possible growth mechanism was also discussed.