The oxidation behavior for in situ synthesized MoSi₂－SiC composites with different SiC volume fraction at 500℃ was investigated. The results of oxidation for 1000 h indicate that the oxidation resistance for composites is significantly higher than that of monolithic MoSi₂, MoSi₂－30%SiC composite in situ synthesized possesses higher oxidation resistance compared with the traditional composite which is fabricated by hot－pressing the mixture of commercial powders of MoSi₂ and SiC. After oxidation for 1000 h, the composites have not been observed to disintegrate (pest). The oxidation kinetics curves are divided into three stages: incubation period, rapid oxidation period and the steady－state. The oxide scale consists of MoO₃, amorphous silica and β－SiC, therefore, the oxidation of the materials is mainly done between MoSi₂ and O₂, and SiC is not oxidized. The surface morphology observations of samples oxidized for 5, 10 and 20 h show that the phase boundary is the preferential oxidation site, the oxides formed at the initial stage of oxidation are irregular－shaped, and MoO₃ whisker and oxide cluster mainly composed of amorphous SiO₂ come gradually into being along with the development of oxidization. It is also found that the nucleation and growth of MoO₃ whisker preferentially take place at the concave and convex sites of substrate surfaces.