The high temperature oxidation behaviour of ferritic stainless steel SUS 430 was investigated over the temperature range from 1000 to 1150 °C in humid air containing 18% water vapour. Isothermal thermogravimetric analyses were performed to study the oxidation kinetics. The microstructure, composition and thickness of the oxide scale formed were investigated via optical microscopy (OM), X-ray diffraction and a scanning electron microscope equipped with an energy dispersive spectrometer. The results indicate that breakaway oxidation occurs at all temperatures and that its onset is accelerated by increasing temperature. The growth rate of the multilayer oxide scale follows a parabolic law with apparent activation energy of 240.69 kJ/mol, and the formation of FeO is decreased when the temperature is higher than 1120°C. The inner oxide scale, Fe-Cr spinel, grows mainly inward and internal oxidation is observed even in a short oxidation test at 1150 °C for 105 s. The mechanism of high temperature oxidation of SUS 430 in humid air containing 18% water vapour is discussed.