A mesoporous composite of magnetic carbon microspheres (MCMSs) was synthesized via introducing Fe3O4 nanoscale particles to the surface of carbon microspheres (CMSs) by coprecipitation. Scanning electron microscopy and transmission electron microscopy showed the Fe3O4 nanoscale particles were dispersedly immobilized on the surface of CMSs. The MCMSs demonstrated effective removal of selenite (Se(IV)) from wastewater. MCMSs showed the regular pattern where the lower pH value, the lower residual Se(IV) concentration. The coexisting sulfate, nitrate, chloride, carbonate, and silicate had no significant effect on Se(IV) removal, whereas phosphate hindered the removal of Se(IV) by competing with Se(IV) and formed inner-sphere complexes with Fe3O4 on the surface of MCMSs. Through X-ray photoelectron spectroscopy analysis, Se(IV) can not only form inner-sphere complexes with MCMSs, but also be reduced to insoluble elemental selenium (Se-0) by Fe3O4 which was oxidized and formed gamma-Fe2O3. Moreover, the superparamagnetic MCMSs can be easily separated from solution by means of an external magnetic field. The high removal efficiency for Se(IV) and rapid separability of MCMSs made them promising materials for the application in the practice. (C) 2017 Elsevier B.V. All rights reserved.