Microstructure evolution of Ni-based superalloy GH202 after oxidation from 800 °C to 1100 °C was investigated. The results show that the hardness of GH202 decreases with the increase of oxidation temperature, and the hardness is decreased by 43.5% after oxidation at 1100 °C for 100 h. The growth rate of the grains after oxidation at 800 and 900 °C is slower and the grains increase slightly at 900 °C. The grain size increases significantly after oxidation at 1000 and 1100 °C, and many fine grains are annexed to form large grains due to grain boundary migration and elemental diffusion during the recrystallization at high temperatures for above 100 h. The big block carbides (MC) decompose into a large number of carbon atoms which combine with Cr atoms to form a few Cr-rich granular M₂₃C₆. After oxidation at 900 °C for 150 h, the M₂₃C₆ evolves into Ti-rich M₆C. With the increase of oxidation temperature, the carbides almost melt into γ phase. Moreover, the γ' phase gradually grows up after oxidation at 800, 900 and 1000 °C, and it is completely dissolved into the γ phase after oxidation at 1100 °C for 100 h.