Using dense medium plasma technology, carbon magnetic nanoparticles (CMNP) were synthesized at room temperature and atmospheric pressure. Based on results from X-ray photoelectron spectroscopy, Fourier transform infrared spectroscopy and scanning electron microscopy, we conclude that these nanoparticles are composed of spherical particles, 40-50 nm in diameter, with iron/iron oxide particles dispersed in a carbon-based host-structure. Thermal gravimetry/differential thermal gravimetry analysis shows these nanoparticles are stable to temperatures as high as 600 degrees C. The synthesized CMNP were treated by argon-plasma, aminated with ethylene diamine and subsequently activated by generating aldehyde groups on them. Free doxorubicin (DOX) molecules were then immobilized onto the surfaces of activated CMNP particles to form CMNP-DOX conjugates. The corresponding loading efficiency was determined. The in vitro antiproliferative activity of immobilized doxorubicin in the conjugates was demonstrated in tumor cell cytotoxicity assays. It is suggested that this CMNP-DOX system can be used for targeted drug-delivery systems.