In the present work, intermetallics Fe3Si and Fe3 (Si1-xAlx) (x=0.33, 0.67, 0.80) produced by arc melting, were evaluated regarding the oxidation at 900°C in air. The test preformed was the isothermal and cyclic oxidation. The microstructures of oxide films were analyzed by XRD, SEM, EDS, EPMA. The result showed that the four kinds of intermetallics had good oxidation resistance at 900°C.The addition of Al element can increase the oxidation resistance of Fe3Si based intermetallics. The oxidation kinetics of the four intermetallics follows the rule of the parabola. The main oxidation product of Fe3Si is SiO2.The kinetics of oxidation reaction is mainly controlled by Si diffusion. The oxidation product of three Al alloying Fe3Si based intermetallics is Al oxide. Al moves outward from the substrate to form a protective oxide film which restrained the diffusion of Si and Fe outward.