Abstract: The oxidation kinetics and the oxidation layer of a cast Ni-base superalloy K35 at 800°C were studied by still TGA method. The results show that oxidation kinetics of the superalloy K35 obeys the parabolic law. The oxidation stage can be divided into two parts within 100 h: the oxidation rate are 2.50×10^-7 mg²/cm⁴·s in first stage and 2.05×10^-7 mg² /cm⁴ ·s in the other stage. Because the average oxidation velocity is 0.00263 mg/cm·h for 100 h, the oxidation resistance of the superalloy K35 is the first grade. It is suggested that oxidation rate of the superalloy K35 is dependent on the growth dynamics of Cr2O3. The oxide layer was examined by X-ray diffraction, scanning electron microscopy (SEM) and energy spectrum analysis (ESA). The layer is thin and consists of Cr2O3 mainly with a bit of NiCr2O4 and TiO·TiO2. During oxidation at 800°C, the inner oxidation occurs in the superalloy.