The separate phases present in a Ni-base superalloy may offer different resistance to hot corrosion attack. Ni-Cr, Ni-A1, and Ni-Cr-A1 alloys of composition corresponding, respectively, to the nominal ,y matrix, the ~' phase, and a system of both these two phases, were coated with Na2SO4 and exposed to oxygen or H2S-H2 gas mixtures in the temperature range 850~176 The corrosive attack was monitored with a recording microbalance. The results indicate that the degree and mechanism of corrosion of the above phases is markedly influenced by the nature of the environment and the composition of the oxide scales formed at the alloy surface, in general, the ~,' phase appears to be a weak link in the over-all hot corrosion process.