A kinetic investigation of corrosion of nickel in hydrogen chloride gases containing 0–75% oxygen at 400–700°C was carried out by the thermogravimetric method. There was no great difference in the corrosion behaviour of nickel in the hydrogen chloride gas and its mixtures with oxygen because of exclusive formation of NiCl 2 scale, regardless of the gas compositions. The corrosion behaviour showed the mixed reaction mode; that is, NiCl 2 scale formation according to parabolic kinetics and NiCl 2 scale evaporation according to linear kinetics. With increasing temperature above 500°C, linear kinetics became predominant.