A network-like porous layer on titanium was prepared by acid-etching with a mixture of CaCl2 and HCl. The pores ranged from 1 to 10!m. The small pores distributed in big pores. In the simulated biological environment, porous octacalcium phosphate (OCP) coatings spontaneously formed on the porous- surfaced titanium. Pre-calcification after acid-etching accelerated OCP precipitation. The OCP coatings had big pores of about 25!m and small pores of 1~3!m, the latter distributed in the former at different depth.