To improve preferential nucleation of calcium phosphate by attractive interaction between Ca2+ ion in biological fluid and titania surface, negatively charged porous titanium oxide films for implant applications were synthesized by electrochemical process in electrolyte of 1.5 M sulfuric acid containing phosphoric acid as air additive, and the effects of surface characteristics of anodic titania on the formation of bioactive apatite were investigated. More nucleation capability of bioactive Ca-P compound was shown on the anodic film formed in high concentration of phosphoric acid electrolyte compared with lower concentration of phosphoric acid. The incorporated phosphate species were found mostly in the forms of HPO4-, PO4-, and PO3-. (c) 2005 Elsevier B.V. All rights reserved.