Low Young's modulus is attained by controlling phase stability of β (bcc) Ti-Nb-Sn alloys consisting of non-cytotoxic elements, based on experimental results that Young's modulus decreases with decreasing temperature toward α" (orthorhombic) martensitic transformation start temperature (Ms). Cold groove rolled, metastable β (Ti-35%Nb)-4%Sn alloy exhibits low Young's modulus of about 40 GPa at 297 K, measured by the free resonance vibration method. This value is much lower than that of Ti-6%Al-4%V and close to that of human cortical bone. By heating one edge of the groove rolled rod to 573 K for 4 h, hardness and Young's modulus are found to increase significantly at the heated zone and to change depending on distance from the heated zone. The increase in hardness is explained mainly by fine α precipitation and additionally by microstructure refinement through reverse transformation α"→β of deformation-induced martensite. From these results, an advanced stem having high strength at the necked part can be developed for a new artificial hip joint, keeping low Young's modulus at the distal part implanted in a femur.