Nb-15W-18Si-xHf (x = 0, 5, 10 and 15, mole fraction, %) alloys were prepared by arc melting and then homogenized at1 750 ℃ for 50 h. The microstructure and mechanical behaviors, such as Vickers hardness, fracture toughness, room- and high- temperature strength of the alloys were investigated. The microstructure of the annealed Nb-15W-18Si-xHf alloys is composed of large primary NbSS dendrite and fine eutectic mixture of NbSS and M5Si3 silicide. Both the hardness and the fracture toughness show an increase tendency at room temperature with increase of Hf content. The 0.2% compressive yield strength, σ0.2 of the alloys with5 %Hf and 10%Hf are larger than 960 MPa at 1 200 ℃, and about 500 MPa even at 1 500 ℃.