MoSi 2 –CrSi 2 –Si 3 N 4 composite coating on Mo substrate was made by in situ diffusion of Mo chromising and by ammonia nitriding and siliconizing. The oxidation behavior of MoSi 2 –CrSi 2 –Si 3 N 4 and MoSi 2 –Si 3 N 4 coatings at 1600°C in air was investigated in detail. Phase constitution and microstructure of the coatings were analyzed by scanning electron microscopy (SEM) with energy dispersive spectroscopy (EDS) and X-ray diffraction (XRD). Although mainly enriched on the surface, the Cr element in the MoSi 2 –CrSi 2 –Si 3 N 4 coating inhibits the diffusion of Si and the formation of volatilizable MoO 3 phase during oxidation. Thus MoSi 2 –CrSi 2 –Si 3 N 4 coating exhibits better oxidation resistance than MoSi 2 –Si 3 N 4 coating.