Superplastic-tensile test and superplastic forming for the denture base (One of the dental parts) were carried out experimentally using an α + β two-phase type Ti-6Al-4V alloy with an ultra-fine grained structure (grain size: 0.3-0.5 µm) obtained through protium treatment. The ultra-fine grained material exhibited a significant superplastic elongation of over 9000% at 1123 K and a flow stress lower than that of coarsegrained material made from the same alloy without protium treatments. Superplastic forming was successfully used to fabricate a denture base without cracks on the surface. These materials may be applicable as biomaterials in medical industries.