Quasi-static tensile properties, deformation and fracture behaviors of both quenched and aged U-5.7%Nb alloys in a temperature range from room temperature to 800 oC were investigated. The results show that the second yield phenomenon of both quenched and aged U-5.7%Nb alloys occurring at room temperature disappeared at a temperature higher than 200 oC, and the embrittlement behaviors of two alloys appeared at 400 oC. Meanwhile, the superplasticity has been observed in two alloys at the temperature higher than 700 oC, and the superplasticity of the quenched alloys was more evident than that of the aged alloys. The microstructures of the aged U-5.7%Nb deformed at quasi-static tension, Hopkinson tension and expansion loadings have been analyzed. The results indicate that the dimples at the center zone of the specimens were more obvious than that at the rim zone in aged U-5.7%Nb alloys fractured at different strain rates. And the grains at the fracture of Hopkinson tension were larger than that of the quasi-static loading. Shear fracture, rim cracking and inclusion falling off were observed in the fracture of the alloys deformed at expansion loading