Hydroxyapatite (HAp) coatings were prepared using electrochemical deposition and post-hydrothermal synthesis. The composition and morphology of coatings at each processing step was studied through the application of scanning electron microscopy (SEM), X-ray diffraction (XRD) and infra-red spectroscopy (IR). The mechanism and kinetics of hydrothermal synthesis were considered in particular, and the influence of the temperature and time on the HAp formation rate was also investigated. The results show that the electrochemical deposition coatings are composed of CaHPO42H2O crystals which are converted into needle-like HAp crystals after post-hydrothermal treatment. The HAp content of the coatings increases with the treatment temperature and time. The synthesis rate also increases with the pH value of the water. The formation of HAp coatings is considered to be a combination of several reactions. An Arrhenius relationship was found between the HAp formation rate and the temperature, and an apparent activation energy of 94.4 KJ/mol was obtained by calculation.