Abstract: Zr-Sn-Nb-Fe alloy specimens tempered at 500 and 560 ℃ with different time after cold rolling, respectively, were exposed to 70 μg/g Li⁺ LiOH solution at 350 ℃, 16. 8 MPa. The microstructures and second phases were examined by transmission electron microscopy (TEM). It is found that the specimen treated by 500 ℃/100 h has the best corrosion resistance among all the specimens. TEM analysis of the specimens tempered at 500 ℃ with different time shows that the second phase changes from the seriate strips to the banding particles with the increasing of tempering time, and the fine βNb particles precipitates from the matrix as tempered to 100 h. The transformation process of specimens tempered at 560 ℃ is similar to those tempered at 500 ℃ except the shorter transition time，and the matrix is recrystallized to the equiaxed grain completely as tempered to 10 h.