Si 3N 4 thick coating was fabricated by reactive RF plasma spraying, in which elemental Si reacted with surrounding nitrogen plasma. It was possible to fabricate the Si 3N 4 coating by reactive spraying on a graphite substrate. As for the substrate, however, graphite is difficult to apply to the practical structural parts because of its low mechanical strength. Thus, it was necessary to realize Si 3N 4 coating onto the metal substrate. In this research, Ti alloy, carbon steel and Ni alloy were used as the metal substrates. Ti alloy was difficult to apply to the formation of Si 3N 4 coating because the preferential reaction of Ti-N prevented the nitriding reaction of Si-N. On the carbon steel substrate, pure Si coating was fabricated. However, nitriding reaction was difficult to occur on this substrate because the melting point of carbon steel was lower than the reaction temperature of Si-N. Ni alloy, one of the useful heat-resistant alloys, was also tried as the substrate. Finally, the feasibility of some kinds of interlayer between Si 3N 4 and steel substrate was clarified to improve the bonding property between Si 3N 4 and metal substrate.