Using magnetic nanoparticles as a drug targeting carrier or imaging agent has attracted attention recently.In this report,a protein drug urokinase (UK) targeted by magnetic nanoparticles will be presented.UK is a thrombolytic agent that has been widely used to treat patients with myocardial infarction but it has also been reported to cause systemic lysis and bleeding side effects.In order to target UK to the thrombus site and reduce its systemic lysis side effect,UK was first immobilized to magnetic nanoparticles (Fe3O4) and then targeted to the site by an external magnet.Magnetic nanoparticles coated with 1,6 hexane diamine were prepared by polyol reduction method and they were further reacted with N-succinimidyl-3-maleimidopropionate to obtain maleimide coated magnetic particle.