The oxidation behaviour of Fe-23Cr-5Al-based alloys unmodified and modified by incorporation, using various procedures, of reactive elements and by implantation of sulphur was investigated at temperatures up to 1673 K, under both isothermal and thermal cycling conditions. The reactive elements, in general, slightly enhanced the oxidation rate of the studied alloy and improved the scale resistance to spalling, these effects being dependent on a few factors. Implanted sulphur did not exert significant influence under studied conditions.