The microstructure, hardness and isothermal oxidation behavior of CoNiCrAlY alloy modified by addition of 3 wt% and 5 wt% Pt were investigated using scanning electron microscopy, Vickers hardness tester, X-ray diffraction and energy dispersive spectroscopy analysis. The results reveal that Pt has a significant influence on the microstructure of the experimental alloy by formation of β-(Ni,Pt)Al phase. Addition of Pt can slightly increase the hardness of the experimental alloys. Pt will accelerate the phase transformation of alumina from metastable θ-Al2O3 to stable α-Al2O3, which is the main reason for the lowering oxidation rate and the formation of a protective oxide scale on the Pt-containing alloys. Furthermore, adding of Pt can improve the Al transport, which suppresses the consumption of β-phase and eliminates the internal oxidation.