Abstract: The specimens of Zr-Sn-Nb alloy with two different composition were treated in different ways as 1 000 ℃-0. 5 h, 1 000℃-0. 5 h/560 ℃-10 h, 1 000 ℃-0. 5 h/C. R. (cold rolling)/560 ℃-10 h and 750 ℃-0. 5 h, 750 ℃-0. 5 h/560 ℃-10 h, 750℃-0. 5 h/ C. R. /560 ℃-10 h, respectively. Their microstructures were examined by transmission electron microscopy (TEM), and the corrosion resistance was investigated with autoclave tests in 0. 04 mol · L-1 LiOH aqueous solution at 350 ℃, 16. 8 MPa. It shows that the corrosion resistance of specimens treated by 750 ℃-0. 5 h/C. R. /560 ℃-10 h is the best among all specimens treated in different ways in present study. A lower niobium concentration in solid solution in αZr matrix and a uniform distribution of fine αNb (containing iron) particles are important factors for improving the corrosion resistance significantly, especially, the later one is more important. Chromium, if it is contained in the alloy, will go with iron to form Zr(FeCr)2 second phase particles at first, then the cor- rosion resistance decreases due to the depletion of iron in the βNb fine particles. The cold deformation before the final annealing at 560℃ plays an important role in obtaining fine βNb particles because which can promote the nucleation during the *Zr decomposition.