In recent years, cancer therapies with nanoparticles have become very important because of their potential use in hyperthermia as well as targeted delivery.For these applications, the highly specific, efficient, and rapid internalization ofnanoparticles into specific target cells is necessary.In this work, we focused on the surface charge of as-synthesized magnetite nanoparticles as a factor controlling their internalization into cancer and normal cells in view of future application in magnetic hyperthermia.We synthesized magnetite nanoparticles by hydrolysis in an aqueous solution containing ferrous chloride with organic amines as a base.It was demonstrated that the difference in surface charge of magnetite nanoparticles brought about the difference in uptake efficiency.We found that the nanoparticles with positive charge showed higher internalization into human breast cancer cells than the nanoparticles with negative charge, while the degree of internalization of the positively-and negatively-charged nanoparticles into human umbilical vein endothelial cells was almost the same.We also synthesized chitosan-coated magnetite nanoparticles and investigated its use as a non-viral gene transfection agent for stem cells.The transfection efficiency of this magnetite-chitosan nanocomposite will be reported.