An experimental study was conducted to study the effects of properties of in-flight particles on microstructures of coating layers using a wire arc spraying system. In this study, 0.8% carbon steel wires were used for arc spraying and nitrogen gas was used as atomizing gas. Temperature, velocity and distributions of the in-flight particles were measured by DPV2000 for different working conditions. Specimens of spray-footprint were made and microstructures of them were evaluated. As a result, amount of oxide in a coating layer was proved to be related with the temperature of the in-flight particles. Because oxidation of the molten steel particles is an exothermic reaction, higher temperature of the particles during arc spraying means higher area fraction of oxide in the coating layers. For this reason, oxide level is lowest at the central area of spray footprint and it becomes higher as the distance from the center increases. Hardness, porosity and phase are changed according to the distance from the center. Abstract only; no full-text paper available.