Oxygen-containing functional groups can be introduced onto the surface of polycrystalline boron-doped diamond (BDD) electrodes by either anodic polarization or oxygen plasma treatment. Of these, the hydroxyl groups are of particular interest and can be studied specifically by means of specific chemical modification with 3-aminopropyltriethoxysilane (APTES). The modification of the surface hydroxyl groups with APTES accelerates the [Fe(CN)(6)](3-/4-) redox reaction, compared to the retardation by the oxidized surface. These changes can be explained in terms of changes in the electrostatic interaction between the surface functional groups and the [Fe(CN)(6)](3-/4-) anion. In particular, electrostatic attraction between [Fe(CN)(6)](3-/4-) and protonated amino groups at the APTES-treated surfaces should be responsible for the acceleration. These results, as well as those obtained in contact angle measurements and X-ray photoelectron measurements, indicate that hydroxyl groups are generated on the oxidized BDD surfaces and that they can be modified with silane coupling agents for introduction of various functionalities onto the BDD electrode surface.