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Due to its good biocompatibility and its high corrosion resistance, Platinum and its alloys have been widely used in implantable medical devices, including neurovascular devices, cardiac rhythm management devices and neurological devices. Implantable neurostimulators have provided therapies to patients with chronic pain, movement disorders, and overactive bladder symptoms. For these therapies, well-controlled stimulation current is delivered to the target nerves through implantable leads. The implantable leads must have sufficient fatigue durability to last for many years of implantation. Although coils made with Pt-20Ir wire have been widely used in conductor leads from major medical device companies, its fatigue performance and microstructure has not been well studied. In this study, a newly developed axial fatigue test method was used to study the fatigue behavior of Pt-20Ir coil, and the fatigue behavior of the corresponding Pt-20Ir wire was studied using a rotary beam fatigue testing method. The fracture surfaces of Pt-20Ir wires and fractured coil filars were analyzed in SEM and compared. The slanted fracture surface was observed for Pt-20Ir coils, indicating that the axial fatigue of Pt-20Ir is multiaxial in nature. Multiaxial fatigue theory should be used to analyze coil axial fatigue behavior. The microstructure of Pt-20Ir cold worked wire for coil was also studied. The detailed microstructure such as crystallography texture and grain structures was analyzed by using SEM/EBSD method.