Dextran was formed on the surface of hydroxyapatite by the enzymatic reaction of dextransucrase to control protein adsorption. The hydroxyapatite substrate was immersed in a dextransucrase solution (0.3U/mL, pH 5.5) to immobilize dextransucrase to the hydroxyapatite surface at 6.0U/mL. The dextransucrase-immobilized hydroxyapatite was then reacted with a sucrose substrate to generate dextran from the active sites of the immobilized dextransucrase. The amount of dextran produced changed with reaction time and substrate concentration, generating dextran at a maximum of 50mg/g. When the proteins, bovine serum albumin and γ-globulin, were adsorbed to the surfaces of both hydroxyapatite and dextran-generated hydroxyapatite, the amount of protein adsorbed decreased with increasing amount of dextran produced, indicating that the protein did not reach the adsorption sites of hydroxyapatite as a result of steric exclusion by dextran. The protein adsorption performance revealed that the generated dextran on HAP can size-exclude proteins.