In order to improve the high temperature oxidation resistance of Fe-Cr alloy, cast Fe-Cr alloys with different Cr contents are treated by electrospark deposition to get microcrystalline structure. The oxidation behavior of as-cast and microcrystalline Fe-Cr alloys at 900 ℃ in air is studied. Oxidation kinetics curves, phase analysis,surface and cross section morphology results show that the diffusion rate of chromium is enhanced by microcrystallized treatment when Cr content is low. Yet the content of Cr is not enough to form continuous oxide film so that the oxidation resistance of Fe-5Cr alloy is decreased. The critical Cr content to form protective oxide scale is reduced by microcrystallized treatment when Cr content increases. The oxidation resistance of microcrystalline Fe-9Cr and Fe-13Cr alloys is obviously improved. The high temperature oxidation resistance of microcrystalline Fe-13Cr alloy is the best, which is due to the formation of continuous dense protective oxide scale on the surface after microcrystallized treatment. Therefore, Microcrystallization treatment is an effective way to improve high temperature oxidation resistance of materials which can be applied in the field of high temperature oxidation.