The mechanics properties of U-2.5%Nb alloy from –100 to 700 ℃ were studied. The results show that alloy tensile strength decreases with the temperature increasing, The plasticity isn’t monotone change below 600 ℃, and the elongation ratio and the area reduction ratio obtain the minimums value near 500 ℃. The tensile fracture morphology along grain boundary rupture presents obviously contrast room temperature, and the plasticity increases obviously beyond 600 ℃. Upon heating up to 500 ℃, for 1 h and then cooling to room temperature(20 ℃)，the impact toughness of the alloy decreases in contrast to no heating up. In the range of –100 ℃～room temperature, the impact toughness of the alloy decreases with the temperature decreasing, the ductile-brittle transition temperatures of U-2.5%Nb alloy is in the range of –30～–10 ℃, the trend mentioned above becomes weak below –30 ℃. The fracture plane is irregular after the impact test, which has a rupture characteristic of quasi-cleavage.