The apatite-forming ability of titanium oxide film with different structures was investigated in a simulated body fluid(SBF).Three different structures of titanium oxide film were prepared.The dense rutile and amorphous titania gel did not induce apatite formation on their surfaces in SBF solution in 48 hours,whereas the micro porous rutile structure induced apatite formation on their surfaces.This indicates that a specific structure of titania is effective in inducing apatite formation.Such specific structure was assumed in this study to be micro porous structure.The spatially sub micro-scale porous structure of titanium oxide film was an important factor to facilitate the Ca-P nucleation.