In-plant corrosion tests were carried out in two coal gasification plants. This research was sponsored by the Agency of Industrial Science and Technology and the New Energy and Industrial Technology Development Organization (NEDO). At the HYBRID pilot plant (fluidized-bed gasifier), the test programme was conducted to evaluate the low temperature corrosion behaviour of construction alloys. The corrosion rate is strongly dependent on the temperature and peaks at about 300°C. At the HYCOL pilot plant (entrained-bed gasifier), the main purpose of the test programme was to obtain corrosion data on candidate heat exchanger tubing alloys. The test alloys were carbon steel, Cr-Mo steels, austenitic stainless steels, Ni-base alloys and diffusion coatings. According to the first examination results from the heat recovery boiler, the corrosion resistance of the test alloys increases with Cr content in the alloy. Cr-Mo steels are severely attacked through sulfidation and austenitic stainless steels are slightly attacked through oxidation and internal sulfidation.