AbstractA thin hydroxyapatite (HA) layer was coated on a microarc oxidized titanium (MAO‐Ti) substrate by means of the sol–gel method. The microarc oxidation (anodizing) enhanced the biocompatibility of the Ti, and the bioactivity was improved further by the sol–gel HA coating on the anodized Ti. The HA sol was aged fully to obtain a stable and phase‐pure HA, and the sol concentration was varied to alter the coating thickness. Through the sol–gel HA coating, the Ca and P concentrations in the coating layer increased significantly. However, the porous morphology and roughness of the MAO‐Ti was altered very little by the sol–gel treatment. The proliferation and alkaline phosphatase (ALP) activity of the osteoblast‐like cells on the MAO/HA sol–gel‐treated Ti were significantly higher than those on the MAO‐Ti without the HA sol–gel treatment. © 2005 Wiley Periodicals, Inc. J Biomed Mater Res 73A: 48–54, 2005