Effect of grain diameter on Young's modulus and tensile properties was investigated using a representative titanium alloy with self-tunable Young's modulus, Ti-12Cr alloy for use in spinal fixation devices. The grain diameter can be changed systematically by changing solution-treatment temperature. With increasing grain diameter, the changes in Young's moduli of the alloys subjected to solution treatment are negligible. Additionally, with increasing grain diameter, the increases in Young's modulus during deformation are almost same. It indicates that the deformation-induced ω phase transformation is not sensitive to the grain diameter. Further, the strengths of the alloys decrease slightly, while the ductility of the alloys decreases drastically as increases in grain diameter. Therefore, a small grain diameter is preferred for developing new titanium alloys with changeable Young's modulus for use in spinal fixation devices.