Magnetic carbon nanotubes consisting of multi-wall carbon nanotubes (MWNTs) core and Fe3O4 shell were successfully prepared by in situ thermal decomposition of Fe(acac)(3) or FeCl3 or Fe(CO)(5) in 2-pyrrolidone containing acid treated MWNTs at 240 degrees C with the protection of nitrogen gas. The samples were characterized by TEM, XRD, SEAD, XPS and superconducting quantum interference device. Also, their biocompatibility was compared with naked carbon nanotubes. The results showed that after coated with Fe3O4 nanoparticles, the obtained magnetic carbon nanotubes show superparamagnetic characteristic at room temperature, and their blocking temperature is about 80 K. The magnetic properties of the nanotubes are relevant to the content of magnetic particles, increasing content of magnetic nanoparticles leads to higher blocking temperature and saturation magnetization. The results of antimicrobial activities to bacterial cells (Escherichia coli) showed that the MWNTs have antimicrobial activity, while the magnetic nanotubes are biocompatible even with a higher concentration than that of MWNTs. (C) 2010 Elsevier B.V. All rights reserved.