Hydroxyapatite　(HA)　is　widely　used　as　surface　coatings　on　biomedical　metal　implants　because　of　its　excellent　biocompatibility　and　osteoconductivity.　In　this　study,　HA　coatings　were　deposited　onto　Ti-6Al-4V　substrates　by　micro-plasma　spraying　and　then　heat　treated　at　650　degrees　C　in　a　muffle　furnace　for　3　h　and　6　h.　XRD　results　showed　that,　the　HA　peaks　were　sharper　than　those　of　corresponding　as-sprayed　coatings　and　the　amorphous　diffuse　background　was　reduced　after　heat　treatment.　The　transformation　from　impurity　phases　such　as　tetra-calcium　phosphate　(TTCP)　and　tri-calcium　phosphate　(TCP)　and　amorphous　calcium　phosphate　(ACP)　to　crystalline　HA　occurred　during　the　heat　treatment.　Moreover,　the　texture　intensity　was　not　increased　during　the　re-crystallization　of　ACP　and　the　transformation　of　impurity　phases　into　HA.　The　SEM　results　showed　that　nanograins　were　formed　on　the　coating　surface.　In　addition,　with　the　increase　of　the　holding　time,　the　nanograins　become　coarse.