Abstract: Carbon-coated iron nanoparticles were synthesized by a carbon arc discharge method using electrodes made of iron and graphite powder. The amorphous carbon layer of the carbon-coated iron nanoparticles was treated by a 30% H2O2 aqueous solution. Adsorption of the carbon-coated iron particles for heavy metal ions, such as Cr, Ni, Cd, Pb, Co and Mn, was studied. Results showed that carboxyl and hydroxyl groups were formed on the surface of the amorphous carbon layer after the treatment by hydrogen peroxide. In a strong alkaline medium, the hydroxyl and carboxyl groups increased the electrostatic attraction, and the adsorption performance of the treated carbon-coated iron particles for heavy metal ions was improved. The removal efficiencies for Cr, Ni, Cd, Pb, Co and Mn by the treated carbon-coated iron nanoparticles were all over 90% in a pH range of 8-10 and their adsorption capacity is much higher than that of activated carbons.