Spatial distributions of temperature and velocity of spray droplets are measured using an optical monitoring system, so as to observe their influences on Al-5Mg coating qualities for three different thermal spray facilities. These are wire arc spray, wire plasma spray, and gas flame spray facilities. Coating qualities investigated are compositions, adhesive strength, porosity, and hardness of coating layers. It has been shown that compositions are strongly influenced by temperature of spray droplets and surrounding shielding gases, and adhesive strengths are dependent on temperature and velocity, while porosities are mostly influenced by velocity. In addition, hardness is shown to depend on the Mg concentrations in the coating layers, which in turn are influenced by temperature of spray droplets and surrounding shielding gases as described above. These observations are discussed from adhesion and formation processes of thermal spray droplets into coating layers.