Three types of magnetic nanopaticles(CoFe2O4，Fe3O4 and CuFe2O4) were prepared by a simple solvothermal reaction and used to remove biological contaminant microcystin-LR in water.Concentrations of microcystin-LR were detected by high performance liquid chromatography(HPLC).CoFe2O4 showed the best adsorption ability for biological contaminant microcystin-LR.Transmission electron microscope,FT-IR,magnetization curve and X-ray diffraction were used to structurally characterize CoFe2O4 nanopaticles which were evaluated to be magnetizable and distributedly homogeneous,with a diameter of about 250 nm.CoFe2O4 nanopaticles and the adsorbed toxin could be separated conveniently from solution with the help of an applied magnetic field.Factors influencing the adsorption capacity including microcystin-LR concentrations,pH conditions,temperature,ionic strength,and the presence of natural organic matter were studied.Adsorption of microcystin-LR on CoFe2O4 increased with the increase of initial concentration and temperature.However,it decreased with the increase of solution pH value and ionic strength.Interestingly,adsorption process was not significantly influenced by the low concentration of humic acid(0-2.5 mg/L),and adsorption ability decreased at higher humic acid concentrations.The results indicated that electrostatic interactions and coordination interactions were important in controlling the adsorption of toxin onto CoFe2O4 nanoparticles.Because of its unique magnetic responsibility,excellent dispersibility in water,and ease in synthesis,CoFe2O4 has a great potential in removing biological contaminants from environmental water.