We report novel magnetic composite nanoparticles for heavy metal ion separation. Superparamagnetic iron oxide nanoparticles (SPIONs) and were coated with poly(methylmethacrylate) (PMMA) by emulsion polymerization process in the aqueous suspension of SPIONs. In addition, the hydrolysis of carboxylic functional groups onto the PMMA-coated SPIONs was grafted with Polyethylene glycol bis(amine). Then, the functional group structures were investigated by Fourier transforms infrared spectroscopy (FTIR). The morphology of PMMA/SPIONs was determined by transmission electron microscopy (TEM) and atomic force microscope (AFM). The magnetic property was investigated by the vibrating sample magnetometer (VSM). The metal concentration in the solution after separation using the nanoparticles was determined by inductivity coupled plasma optical emission spectrometer (ICP-OES). Furthermore, we demonstrate that the efficiencies of the heavy metal ion removal for Cu(II), Mn(II), Zn(II), Cd(II), Pb(II), Co(II) and Ni(II) are 80.0 %, 57.7 %, 54.3 %, 40.0 %, 34.8 %, 32.5 % and 30.2 % by weight, respectively. The nanoparticles also exhibit some selectivity for copper, manganese and zinc. The results show that the composite nanoparticles are extremely promising for heavy metal ion separation.