Hydroxyapatite (HAp) coatings were prepared by a hydrothermal electrodeposition method on Carbon/carbon (C/C) composites. The as-prepared HAp coatings were characterized by XRD and SEM analyses. The influence of hydrothermal temperature on the phase and surface microstructures of HAp coatings and the corresponding deposition kinetics were particularly investigated. Results show that with the increase of hydrothermal temperature, the crystallinity, density and homogenous of the prepared HAp coatings are improved. The deposition rate also increases with the increase of hydrothermal temperature. The deposition activation energy of HAp coatings by the hydrothermal electrodeposition process is calculated to be 25.89 kJ/mol.