Abstract: Magnetic iron oxide nanoparticles are iron oxide particles of nanometer diameter with the characters of steady chemical property, long blood retention time, low toxicity, paramagnetism and biodegradability. Due to the cross-linking to tumor-targeting ligands through electrostatic interaction or chemical coupling such as peptides, monoclonal antibodies, chemotherapeutic drugs, gene segments. They are widely used for clinical oncology imaging, therapy and investigation. This article focuses on the applications and recent developments of magnetic iron oxide nanoparticles for tumor imaging and therapy.