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Self-passivating W-Si-Zr alloys were prepared by mechanical alloying and spark plasma sintering. Microstructures of alloys were characterized by XRD, XPS, SEM and EPMA, and their oxidation resistance was tested. The results show that the alloy contains W-enriched, W₅Si₃, SiO_x (x=1, 1.5, 2) and ZrO_x (x=1, 1.5, 2) phases. The W₅Si₃ phase distributes continuously. SiO_x and ZrO_x particles are dispersed in the matrix with the sizes of 1.0–2.5 μm and 0.7–2.7 μm, respectively, and ZrO_x particles are often associated with SiO_x particles. The W₅Si₃ plays a key role in the oxidation resistance of the alloy. The addition of Zr contributes to the formation of W₅Si₃ phase, whose area reaches 70.2%. The oxidation rate of W-Si-Zr alloy is about 1/2 of that of W-Si alloy and 1/36 of that of pure W at 1000 ℃ in the air.