Film-coating on the surface of titanium was investigated by hydrothermal treatments with a maximal pressure of 6.3 MPa (280°C) in CaO solution and water to improve bioactivity and biocompatibility. As a result, calcium titanate (CaTiO3) film was formed on the titanium surface. The surface-coated titanium was immersed in a simulated body fluid (SBF) to estimate its bioactivity. Apatite precipitation was observed on all hydrothermal-treated titanium surfaces after immersion in SBF for 4 weeks. In particular, the apatite precipitation of titanium treated with 6.3 MPa in CaO solution was clearer and larger in amount than those of all other hydrothermal-treated specimens. The results suggest that surface modification of titanium with high-pressure hydrothermal treatments can be expected to improve bioactivity and biocompatibility.