Ferroferric oxide ，a respresentative of biomedical magnetic nanomaterials, have shown great potential in nanomedicine because of their unique size-dependent properties, easy surface functionalization and good biocompatibility. Recently, great progress in this field has been achieved in materials design and biomedical applications, especially, the iron oxide nanomaterials can be used as intelligent materials to mediate the external field. To highlight these achievements, here we discuss the biomedical applications of magnetic nanoparticles in magnetic resonance imaging contrast agents, magnetic hyperthermia and magnetic force controlled biological effect, magnetotheranostics and nanozymes. With the quick development in nanomedicine, magnetic nanoparticles-based diagnostics and therapeutics are believed to play vital roles in tackling major disease in the future.