Abstract. The study was designed to understand the influence of different atmospheres of plasma gas on hydroxyapatite-coated commercially pure Titanium (Ti) and titanium alloy (Ti-6Al-4V). Ti and Ti-6Al-4V were plasma spray-coated with hydroxyapatite in argon, nitrogen, argon/hydrogen, and nitrogen/hydrogen atmospheres. The microstructure, porosity, calcium to phosphate (Ca-P) ratio, surface roughness, and hardness of the coat were characterized using a scanning electron microscope, energy dispersive spectroscopy, image analyzer, profilometer, and Vickers hardness tester. The analyses of the coatings obtained in different plasma gas atmospheres showed variation in microstructure, morphology, porosity, surface roughness, and hardness. As the enthalpy decreased, an increase in porosity was observed in nitrogen/hydrogen, nitrogen, argon/hydrogen, and argon atmospheres, respectively. Peak Ca-P ratio was observed in argon, which is the most inert atmosphere compared to other tested plasma atmospheres. Atmospheres with high enthalpy presented an even surface with comparatively low surface roughness. Hardness value decreased with increasing porosity. The plasma gas atmosphere has a significant influence on Ca-P ratio, porosity, and microcracks of hydroxyapatite-coated oral implants. Keywords: EDS / implant coating / plasma spraying / SEM / surface characterization