The passivation, oxidation stratified architecture, and mechanical behavior of Al-doped fcc + hcp dual-phase cobalt-based multi-principal element alloys (MPEAs) Co(47.5-x)Cr30Fe7.5Ni7.5Mn7.5Alx (x = 0, 0.5, 1.0, 1.5, 2.0 at.%) at elevated temperatures were studied comprehensively in the present work. The evolution of the surface morphology, specific oxide growth processes, and elemental distributions were analyzed by scanning electron microscope (SEM), energy dispersive X-ray spectrometer (EDS), and X-ray Photoelectron Spectroscopy (XPS). The analyses show that the oxidation kinetics of the Al-doped MPEAs follow the parabolic or near-parabolic law at 600, 800, and 1000 °C. The alloys generally undergo different oxidation stages: for instance, (1) surface reaction between O2– ions and metal ions, (2) surface thickening via oxygen chemisorption, (3) oxide flaking induced by thermal expansion coefficients mismatches. However, no spallation was observed for the present alloys during the 100 h oxidation experiment. The experimental results indicate that the oxide layers have a triple-layer stratified architecture: the outer layer Mn3O4, the intermediate layer (Mn,Cr)xO4, and the inner layer Cr2O3 + Al2O3. CanA2 (Co47Cr30Fe7.5Ni7.5Mn7.5Al0.5) exhibits optimal high-temperature oxidation resistance and demonstrates high strength-ductility at room and elevated temperatures in different processes. The pre-formed Al2O3/Cr2O3 in passive film at room temperature serves as a critical diffusion barrier at high temperature, reducing oxidation rate by 63 % at 1000 °C. This work proposes a surface engineering strategy for designing promising materials with a barrier layer for aerospace engines.