Abstract: U－Nb alloy had good corrosion resistance, structural stability and processability, it was an important structural material in the nuclear field. Quenched U－Nb alloys with different Nb element contents were prepared, and their microstructure and specific heat capacity were studied. The results show that there was a large amount of coarse needle like martensite in the quenched U－2Nb alloy. As the content of Nb element increased, martensite gradually disappearred, and U－Nb alloy formed equiaxed crystal structure. With the increase of Nb element content and temperature, the specific heat capacity of U－Nb alloy gradually increased. When the temperature exceeded 650 ℃,the U－Nb alloy underwent phase transformation and the specific heat capacity significantly decreased.