In order to prepare calcium hydroxyapatite (CaHAp) containing a component with photo-catalytic activities such as Ti 4+ , two preparation procedures, coprecipitation and surface treatment, were investigated since it was recently reported that CaHAp containing Ti 4+ species possessed rather greater activities than the corresponding oxide. The solid produced from the coprecipitation of Ca 2+ , Ti 4+ and PO 4 3− in aqueous phase was not homogeneous due to the precipitation of Ti-species in the solution during the preparation, indicating that a particle of the Ti-species was present in the bulk phase of the hydroxyapatite. Since it is sufficient that the Ti-species is present on the surface of CaHAp in respect to the employment as a photo-catalyst, the surface treatment of CaHAp with Ti 4+ was examined under the dilution conditions of TiSO 4 in acidic solution to avoid the precipitation of the Ti-species. The employment of pH=1.1 was rather unfavorable due to the conversion of CaHAp to CaHPO 4 while the conversion was suppressed by using the solution of pH=1.7. When CaHAp was added to the homogeneous solution containing Ti 4+ by the atomic ratio Ti 4+ /Ca 2+ =1/10, in which the former and latter were corresponded to molar number of Ca 2+ in CaHAp added and that of Ti 4+ in the solution, Ti 4+ was completely immobilized within 30mim. Similar immobilization behaviors were also observed in the immobilization of aqueous Zr 4+ with CaHAp. It was pointed out that the surface of CaHAp treated with Ti 4+ and Zr 4+ was covered with Ca 2+ species since re-precipitation of Ca 2+ species occurred after the immobilization of those tetravalent cations.