A post-treatment of hydrothermal process was conducted to evaluate its effects on the material characteristics and mechanical properties of plasma-sprayed pure HA and HA/20％ YSZ coatings. Surface morphology and microstructural changes, relative element contents as well as phase transformations were analyzed by scanning electron microscopy, energy dispersive spectroscopy, and X-ray diffractometry. Both microhardness and Young\'s modulus were measured. CaCO3 was found existing before and after the whole process of post-treatment. Peaks of impurity phases such as CaO, TCP, and TTCP of as-sprayed coatings were observed to disappear while HA peaks show a tendency of getting higher and wider over time. Surface morphology of SEM analysis presents a clear deposition behavior of ultrafine HA crystallized particles and cross-sectional analysis exhibits a dense and fine structure. Mechanical properties of HA/20％YSZ coatings are found to be significantly higher than those of pure HA coatings and both of which displayed an overall increase with the heating time, indicating enhanced performances.