The magnetic chitosan nanoparticles were prepared by a simple one-step in situ co-precipitation method and characterized by means of X-ray diffraction (XRD), transmission electron microscope (TEM), Fourier Transform infrared spectroscopy (FTIR), vibrating sample magnetometer (VSM) and energy dispersive Xray spectrometer (EDS). The sorption performance of the nanoparticles for removing Cu(II) from aqueous solution was investigated. The experimental results showed that the particles were super-paramagnetic, with the saturation magnetization of about 36 emu/g and the size was in the range of 8-40 nm. The EDS images confirmed the presence of Cu(II) on the surface of magnetic chitosan nanoparticles. The maximum sorption capacity was calculated to be 35.5 mg/g using the Langmuir isotherm model. The mechanism of Cu(II) sorption onto the magnetic chitosan nanoparticles was tentatively proposed. (C) 2011 Elsevier B.V. All rights reserved.