The effect of microstructure with high fraction of Σ3_ⁿ boundaries and serrated grain boundaries (SGBs) on high temperature oxidation of Inconel 617 is studied. After deformation then slowing cooling treatment, the fraction of Σ3_ⁿ boundaries can be increased to over 70% also simultaneously changing some of the rest random grain boundaries (RGBs) into SGBs with the average amplitude of 0.83μm and the average wavelength of 15.98μm. The formation of SGB is associated with the precipitation of Mo₆C和Cr₂₃C₆ carbides at RGB. The microstructure with two types of special grain boundaries (GBs) can effectively improve the high temperature oxidation resistance, which is reflected in significantly reducing the thickness of Cr₂O₃ surface oxide layer and the diffusion depth of Al₂O₃ along the GB. This is attributed to that Σ3_ⁿ boundaries, SGBs and unconnected straight RGB network can effectively retard the diffusion of Cr and O elements along the GB.