An adherent hydroxyapatite (HA) coating was applied onto H2O2-treated carbon/carbon composite (HT-C/C) substrate by induction heating and hydrothermal treatment techniques. Specimens of C/C were initially modified by immersed in an autoclave with 2 M H2O2 solution at 433 K, and then coated with monetite crystals by induction heating method. Subsequently, monetite coating on HT-C/C was converted to HA coating by hydrothermal treatment in an autoclave with the ammonia solution at pH of 10 at 433 K. The compositions, structures and morphologies of the coatings on HT-C/C were analyzed by EDS, SEM and XRD, and the adhesive strength of HA coating on HT-C/C was evaluated by a scratch test. The results showed that the coatings of monetite and HA display no significant changes in their morphologies before and after hydrothermal treatment. They have rectangular crystals stacking one another, and a strong adhesive interface has formed between the HA coating and HT-C/C substrate. The HA coating on HT-C/C was not scraped off until the applied load reached 13.12 N (i.e., shear stress of 61.4 MPa). Crown Copyright (C) 2008 Published by Elsevier B.V. All rights reserved.