Abstract: The isothermal oxidation behavior of microcrystalline Ni-11.5Cr-4.5Co-0.5Al superalloy sheet fabricated by Electron Beam Physical Vapor Deposition (EB-PVD) at 1 000 ℃ in air was investigated in this paper.The oxidation kinetics of microcrystalline superalloy sheet followed a parabolic power law at initial stage of oxidation,and four power law for long oxidation terms.Surfaces and cross-sections of the oxidized specimens were studied by scanning electron microscopy (SEM).Phase identification of the oxide scale was performed by Small Angle X-ray diffraction (SAXD) and Energy Dispersive Analysis of X-rays (EDAX).The fine and compact oxide formed on the microcrystalline superalloy surface grows up with time.The oxide scales consisted mainly of an outer NiO,CoCr2O4 and Cr2O3 mixed oxides.And a continuous inner oxide layer of Al2O3 formed can be observed at 96 h oxidation.