Nanomaterial drug delivery systems are promising vehicles to improve chemotherapy and decrease side effects. In the last years, there have been more reports published in prestigious journals addressing the successful application of magnetite nanoparticles in tumors treatment. The antitumor effect of magnetic fluids was studied intensely by applying an external magnetic field to retain the nanoparticles in the tumor tissue, and also to help regulating the release of loaded drugs. These features make them more competitive as a drug carrier than other nanomaterials. In addition, the MRI (magnetic resonance imaging) property of magnetic nanomaterials can enhance the monitoring of drug carriers locations. In all cases, the tumor significantly regressed in size and the microscopic exam revealed that the tumor cells massively endocytosed magnetic nanoparticles and entered in lysis process. Although the functionalization of nanoparticles generally refers to the addition of a polar shell to increase their solubility on the human body liquids, we have demonstrated that nanomaterials based magnetite functionalized with different types of fatty acids could exhibit antitumor properties without applying any external alternating magnetic field, when tested in vitro, on HEp–2 cells.