Abstract: To improve the oxidation resistance of high-performance NiCrCo medium-entropy alloys for lightweight structural applications at elevated temperatures, porous NiCrCo alloys were fabricated by powder metallurgy combined with spark plasma sintering (SPS). A trace amount of chromium acetate ethanol solution was introduced during powder mixing to regulate oxygen diffusion and realize the in-situ formation and pre-dispersion of Cr2O3 ceramic particles in the alloy matrix. The high-temperature oxidation behavior and oxidation mechanism of the porous NiCrCo alloys were systematically investigated after isothermal oxidation at 700–1100 °C for 20 h. The results show that the porosity of the alloys can be controlled within the range of 6.3 ~ 18.9 % by adjusting the SPS pressure from 3 to 15 MPa, and that Cr2O3 particles are uniformly distributed along the pore edges. The oxidation products exhibit an obvious temperature-dependent evolution with increasing oxidation temperature. A continuous protective Cr2O3 layer is mainly formed at the oxide scale/substrate interface, while the contents of the spinel oxides NiCr2O4 and CoCr2O4 gradually increase with increasing temperature. Based on the porous structural characteristics, phase evolution and microstructural changes during oxidation, the high-temperature oxidation mechanism of the porous NiCrCo alloys was revealed. The preformed Cr2O3 ceramic phase regulates oxygen diffusion and improves the stability of the oxide scale. The results indicated that the deliberate introduction of a protective oxide ceramic phase could effectively regulate the high-temperature oxidation process of the alloy and alleviate oxidation-induced performance degradation, providing a new approach for the design of lightweight structural materials for high-temperature applications.