Due to their inherent magnetic properties and multifunctional design, magnetic nanoparticles (MNPs) fall within a category of highly customizable instruments that can be utilized as imaging agents, medicinal medications, biological devices, nano-electronic biosensors, or molecular nanotechnology for the delivery of drugs and genes. Human biosafety (HBS) of MNPs for clinical usage has grown to be a significant concern as the configuration, shape, chemical characteristics, and implant locations, along with their possible uses, become increasingly complex. Health hazards could also arise if MNPs build up in the cells or organs of humans or interact with their particles or chemical constituents. Consequently, this chapter reviews the special physical and chemical features, possible medical applications, as well as HBS in clinical studies of MNPs. Finally, the chapter will attempt to look at the challenges of practical translation and the prospective applications of MNPs in the biomedical fields. In conclusion, this chapter makes some recommendations for further study in nanomedicine.