The coatings formed on the H2O2-treated titanium substrate by electrodeposition were used in order to evaluate the difference of transformations in the simulated body fluid (SBF) and the culture medium with MG63 cells. A porous hydroxyapatite (HA) coating with relatively low crystallinity and large crystallites was formed on the H2O2-treated titanium substrate by electrodeposition. HA coating transformed for 5 days in the SBF consisted of densely-packed rod-shaped crystallites with various differentiated grains. Octacalcium phosphate (OCP) and HA coating transformed for 5 days in the culture medium consisted of both flake-shaped and rod-shaped crystallites with indistinct grains. MG-63 cells were well attached and proliferated during the transformation into this flaked-shaped OCP. This difference between transformations of the HA coatings in the acellular SBF and in the culture medium with MG63 cells is due to different ion composition in each solution and proteins in culture medium.