The plasma-sprayed metallic powder deposits contain usually some amounts of oxides originating from a gas-liquid reaction after melting the particles flying in the plasma plume, and a gas-solid reaction after the particle impact and solidification. In the present paper, a model of the in-flight oxidation of molten metallic paricles is described. Only the growth of a continuous oxide layer on the molten particle surface is assumed, whereas melt convection and oxide nodule formation inside the particles are not taken into consideration. The model is applied to spraying of pure iron powder by a water-stabilized plasma gun. After the presumed flight time, the calculated and measured values of the oxide thickness are of the same order of magnitude.