A process for producing a medical instrument, such as a stent and a guide wire, which has an excellent fatigue life; and a medical instrument, such as a stent and a guide wire, which has an excellent fatigue life. The process for producing a medical instrument includes: a preparation step of preparing a medical instrument including a NiTi-based alloy as a base material; and an ion irradiation step of irradiating the medical instrument prepared in the preparation step with Xe ions. The medical instrument is produced by irradiating a medical instrument including a NiTi-based alloy as a base material with Xe ions.