Carbonate calcium hydroxyapatites (CAP) containing various amounts of carbonate ions from 0 to 10.1 wt.% were synthesized, and the adsorption behavior of bovine serum albumin (BSA) on these synthetic CAPs was investigated at pH 6.0 and 15 degrees C. The size of the synthetic CAP particles decreased by uptaking CO2-3 ions. The FTIR spectra of CAPs revealed that the CO32- ions are substituted for both OH- and PO43- ions. However, no remarkable difference was detected among the surface properties of these CAPs. The adsorption isotherms of BSA on CAPs were pseudo-Langmuir type. The saturated amounts of adsorbed BSA (n(s)), which is the plateau value of the adsorption isotherms, decreased with an increase in CO32- ion content in CAPs. This fact could be explained by the difference in the particle textures of CAPs, the large rod-like particles with flat surface are advantageous for the adsorption of negatively charged BSA by the large number of positively charged adsorption sites on the exposed ac or be crystal planes. It was considered therefore that the particle texture is significant in the adsorption of BSA.