MoSi2-B4C composite coatings were prepared on Nb alloy by spark plasma sintering process. Pure Mo, Si and B4C powders were used as the coating starting materials. The microstructure formation process and interface reaction characteristics of the coatings during SPS were studied. The oxidation resistance of the coatings at 1450℃ was investigated. The results showed that the MoSi2 phase formed completely in the coatings during the heating stage of sintering, and the B4C particles reacted with the neighboring MoSi2 to form SiC and Mo2B5 at the initial stage of holding time. During the sintering process, elements Si and B diffused inwardly from the coatings to the Nb substrate, forming an interdiffusion zone composed of NbSi2+ NbB outer layer and Nb5Si3 inner layer. The coatings could protect Nb alloy effectively from oxidation at 1450℃ for at least 100h, and dense SiO2-B2O3 oxide scales were formed on the surfaces of the coatings. The presence of NbB in the interdiffusion zone effectively impeded the inward diffusion of Si in the coating during the oxidation process.