The oxidation resistance of FexSi metallic coatings, with x=17, 25, 35, 45 and 75% in weight, have been evaluated in pure O2, in the temperature range of 600–900°C after exposure for up to 24 h. The substrate was a 304 type stainless steel, and between the alloy and the coating a Ni20Cr coating was used to improve the adhesion of the Si-base. The coatings were applied with a powder flame spraying gun. The Ni–20%Cr thermal spray coating had the lowest oxidation resistance, followed by the FexSi coating. The uncoated 304 type stainless steel had the highest oxidation resistance. The FexSi coatings had a higher oxidation rate than the 304 type stainless steel due to the fact that the coatings had a very high porosity regardless of the content of Si and also to the fact that the diffusion coefficients for Si in Fe–Cr alloys is at least two orders of magnitude lower than that of Cr, so the time required to form a protective SiO2 layer is much longer than the one for Cr2O3. There was no major effect of the Si content in the metallic coatings on their oxidation resistance in the range of temperatures tested here. The Ni–20%Cr has a higher oxidation rate than the uncoated 304 type stainless steel, although the Cr content is very similar in both of them, due to the fact that the Cr diffuses much faster in Fe–Cr than in Ni–Cr alloys, and the solubility and diffusivity of O2 is higher in Ni–Cr than in Fe–Cr alloys.