Abstract : This paper reports a magnetically controlled tethered microrobot, designed to enhance the steering of a medical guidewire in complex vascular structures during minimally invasive interventional procedures. The microrobot is composed of ferromagnetic materials incorporated in a silicone tube and is tethered to a guidewire. The steering and navigation capabilities of the fabricated microrobot were tested in a tortuous vascular phantom model in vitro where the results showed that the microrobot was able to precisely steer the guidewire to the designated target sites in a selective manner. In addition, the microrobot was manipulated in the blood vessels of a swine model to assess its efficacy in in vivo environments. With the help of a magnetic control system and an imaging modality, the proposed microrobot will be able to assist medical physicians with guidewire manipulation to reach hard-to-reach target lesions for the treatment of various vascular diseases.