Superparamagnetic Fe3O4 nanoparticles have been successfully synthesized under hydrothermal condition with the assistant of ionic liquid 1-hexadecyl-3-methylimidazolium chloride ([C(16)mim]Cl). The structure and morphology of the sample have been investigated by X-ray diffraction (XRD), X-ray photoelectron spectra (XPS), transmission electron microscopy (TEM), and high-resolution TEM (HRTEM), and the results indicate that the as-synthesized inverse spinel Fe3O4 nanoparticles have an average diameter of about 10 nm and exhibit relatively good dispersity. More importantly, it is found that [C(16)mim]Cl acts as stabilizer for the Fe3O4 nanoparticles by adsorbing on the particles surfaces to prevent the agglomeration. In addition, the obtained superparamagnetic Fe3O4 nanoparticles have a saturation magnetization of 67.69 emu/g at 300 K. (C) 2014 Elsevier Ltd. All rights reserved.