present, the three dominant metallic alloys used as biomaterials are Co-Cr alloys, stainless steels, and Ti alloys, and Mg alloys provide a biodegradable option. [1][2][3] There are basically three qualities required of a metallic biomaterial: good biocompatibility, high corrosion resistance, and good wear resistance. Recently, the need for a low Young's modulus similar to that of human bones has been highlighted. A large difference in the Young's modulus of the implant and the bone has been shown to result in the loosening of implants and bone atrophy due to the "stress shielding effect." [2,4] At 190-240 GPa, the Young's modulus of the Co-Cr alloys and stainless steels commonly used at present is much higher than that of the 10-30 GPa of human bones. [2,5] Many kinds of β-type Ti alloys with a body-centered-cubic (BCC) structure and a relatively low Young's modulus have been developed. [1] The Young's modulus of these polycrystalline alloys is typically in the range of 50-80 GPa. [1,2] The Young's modulus of a single-crystal Ti-Nb-Ta-Zr has been reported to be 35 GPa in the <001> direction, [6] and a low apparent Young's modulus of 20 GPa has been shown for some Ti-Nb-based alloys when stress-induced martensitic transformation is involved. [7] While these alloys are appropriate for use as the stems and the acetabular cups of totalThe demand for biomaterials has been increasing along with the increase in the population of elderly people worldwide. The mechanical properties and high wear resistance of metallic biomaterials make them well-suited for use as substitutes or as support for damaged hard tissues. However, unless these biomaterials also have a low Young's modulus similar to that of human bones, bone atrophy inevitably occurs. Because a low Young's modulus is typically associated with poor wear resistance, it is difficult to realize a low Young's modulus and high wear resistance simultaneously. Also, the superelastic property of shape-memory alloys makes them suitable for biomedical applications, like vascular stents and guide wires. However, due to the low recoverable strain of conventional biocompatible shape-memory alloys, the demand for a new alloy system is high. The novel body-centered-cubic cobalt-chromium-based alloys in this work provide a solution to both of these problems. The Young's modulus of <001>-oriented single-crystal cobalt-chromium-based alloys is 10-30 GPa, which is similar to that of human bone, and they also demonstrate high wear and corrosion resistance. They also exhibit superelasticity with a huge recoverable strain up to 17.0%. For these reasons, the novel cobalt-chromium-based alloys can be promising candidates for biomedical applications.