<p>Mo-Si-B composite coating was successfully prepared on molybdenum substrate by a two-step molten salt electrodeposition, including boronizing and siliconizing. The high-temperature oxidation behavior of Mo-Si-B composite coating was evaluated. The results showed that Mo-Si-B composite coatings prepared under different siliconizing times all presented a double-layer structure with an inner boride layer and an outer silicide layer. The inner boride layer could function as a diffusion barrier to limit the internal diffusion of silicon since the thickness of the outer silicide layer in the composite coating was much less than that of the silicide coating deposited directly on molybdenum. A continuous and dense SiO₂-B₂O₃ composite oxide film was formed on the surface of Mo-Si-B coating after oxidation at 1000&#xa0;°C, which could effectively block the further entry of oxygen. The original boride layer and Mo₅SiB₂ layer formed during oxidation could hinder the internal diffusion of Si and inhibit the degradation of MoSi₂.</p>