Apatite formation on artificial materials in a body environment is the prerequisite condition for showing bioactivity i.e. bone-bonding ability. A specific hydrated silica or titania gel has the ability of apatite deposition in body environment. We electrochemically prepared such a bioactive titanium oxide layer on titanium(Ti) with a cell consisting of Ti as the working electrode, Pt as the counter one, Ag/AgCl as the reference one, and an aqueous solution of 0.1 mol/L Ca(NO3)2 as the electrolyte solution. Ti was kept at 9.5V for 1 hour for oxidation(denoted as Ca9.5). Ti was subject to cathodic polarization at −3.0V for 10 min(Ca-3.0).: calcium ions were expected to be adsorbed on its surface. On treatment Ca9.5–3.0 Ti was first oxidated at 9.5V for 1 hour and subsequently kept at −3.0V for 10 min. The specimens of Ca9.5–3.0 and Ca-3.0 were found so bioactive as to deposit apatite within 12 hours and 1 day, respectively, in a simulated body fluid(Kokubo solution) whereas those due to Ca9.5 could not deposit apatite within 7 days. Calcium hydroxide and calcium carbonate detected on the bioactive surface caused no harmful effects on spontaneous deposition of apatite in the fluid.