The oxidation behavior of two Ni-based superalloys, Inconel-625 (In-625) and Hastelloy X (Has-X) was studied at 750~1050℃ in dry air. The oxidation kinetics of both alloys followed a two-stage parabolic-rate law, indicating that diffusion is the rate-controlling step during oxidation. The steady-state rate constants (k(subscript p) values) of these two alloys were nearly identical. The scales formed on the two alloys were composed of a heterophasic mixture of mostly Cr2O3 and minor MnCr2O4.