It was found that typical Nbss /Nb5Si3 eutectic lamellar structure formed in the Nb-Mo-Si alloy. The interface between Nbss and Nb5Si3 phases was so strong that the alloy fractured mainly in the cleavage mode. In this paper, the fourth element was added with the aim of modifying interface structure. The microstructural characterization and the fracture toughness of Nb-17Si-10Mo ternary alloy doped with Ga, In, Zn and V, respectively, were investigated. It was revealed that the lamellar structure maintained with the addition of Ga and In, whereas it changed slightly with Zn and V additions. Moreover, a little increase in fracture toughness of Nb-17Si-10Mo ternary alloy was obtained through the addition of Ga and Zn. The was found that typical Nbss / Nb5Si3 eutectic lamellar structure formed in the Nb-Mo-Si alloy. The interface between Nbss and Nb5Si3 phases was so strong that the alloy fractured mainly in the cleavage mode. In this paper, the fourth element was added with the aim of modifying interface structure. The microstructural characterization and the fracture toughness of Nb-17Si-10Mo ternary alloy doped with Ga, In, Zn and V, respectively, were investigated. It was revealed that the lamellar structure maintained with the addition of Ga and In, it has changed slightly with Zn and V additions. Moreover, a little increase in fracture toughness of Nb-17Si-10Mo ternary alloy was obtained through the addition of Ga and Zn.