High-temperature oxidation behavior of iron-based superalloy (800H) was investigated at 750°C, 850°C, and 950°C in air for 96 h. Weight gain was used to determine the kinetics of oxidation. The surface of the alloy was characterized by using scanning electron microscopy, X-ray diffraction, and energy dispersive X-ray spectroscopy after oxidation process. The results showed that mass gain increased rapidly in the initial stage of oxidation at high temperature. The alloy obeyed parabolic behavior at 750°C, 850°C, and 950°C. The oxide layer mainly contains oxides of chromium oxide, nickel oxide, iron oxide, and spinel chromium nickel oxide. The thickness of the oxide scales increased with time and temperature.