The corrosion behaviour of several alloys and of various protective coatings on 15Mo3 has been tested under conditions found in coal gasification processes. The experiments showed that of all the uncoated samples tested, only AISI 310 has a promising resistance to these corrosive atmospheres. On most of the other materials spalling of the corrosion products was observed. The main corrosion products were iron, chromium and nickel sulphides, chromium oxide and chromium carbide. Materials protected by different coatings showed very good corrosion resistance when coated by plasma spraying with FeCrAl, containing small amounts of yttrium. Good resistance by coating against the corrosion was also observed for alloys chromized by pack cementation. A small amount of vanadium added to the pack improved the quality of the diffusion coating considerably.