Ni, Ni-Al and Ni-Cr powder particles were plasma sprayed onto the mirror polished metallic substrate surface and the effect of substrate temperature on the particle/substrate interface microstructure was investigated. Sprayed particles were fully melted, sphere in a shape and oxidized on their surfaces during spraying in an air atmosphere. The surface oxide layers were detected as Al or Cr rich thin layer, respectively by electron probe micro analysis (EPMA). After spraying of the particles onto the substrate, cross section microstructures at particle/substrate interfaces were investigated. As a result, almost no oxide layer was detected at the particle/substrate interface when the substrate was kept at room temperature. On the other hand, the oxide layer was apparently recognized at the interface when the substrate was kept at a certain elevated temperature, such as at 673K. The difference in the existence of the oxide layer at interface seems to relate the wettability of the substrate by the liquid particles. The transition temperature, Tt, for each powder material was measured. The meaning of elemental addition to the base metal was considered from the changing tendency in Tt value of each powder material. Through the investigation results obtained, dominating factor on the flattening of the thermal sprayed particles onto the flat substrate surface was estimated.