At present, the development of low-cost Ni-based single-crystal (SX) superalloys with excellent properties is urgently needed to address the increasing cost of advanced aero-engines. In this study, a novel low-cost, third-generation Ni-based SX superalloy containing 3%Re (mass fraction) was investigated to assess its oxidation behavior and γ′ phase degradation at 1120 ^oC. Results showed that during the first 5 h of oxidation, a continuous and uniform three-layer oxide film was formed on the surface of samples. Given the relatively thin oxide film, measured at approximately 5 μm, the experimental alloy followed sub-parabolic kinetics. Between 10 and 100 h of oxidation, the nucleation and propagation of cracks in the Al₂O₃ interlayer accelerated the spallation of protective oxide films. This event resulted in the increased oxidation of the matrix alloy, along with the formation of AlN and large areas in the oxidation reaction domain (ORD). These phenomena caused the transformation from sub-parabolic kinetics to linear kinetics. After 150 h of oxidation, a continuous and zigzagging Al₂O₃ layer was formed at the bottom of the ORD that could hinder the outward diffusion of alloy elements and the inward diffusion of oxygen. Consequently, the alloy gradually approached parabolic kinetics as the Al₂O₃ layer was thickened. In addition, the intense oxidation reaction on the surface accelerated the degradation of the γ′ phase and the precipitation of the topologically close pack phase near the surface. Therefore, the low bond strength between the surface oxide film and the alloy matrix primarily contributed to the deficiency of high-temperature oxidation resistance of this experimental alloy.