[en] The specimens of ZIRLO alloys were treated in different ways at 1000 degree C-0.5 h, 1000 degree-0.5 h/560 degree C-10 h, 1000 degree-0.5 h/C.R.(cold rolling)/560 degree C-10 h and 750 degree C-0.5 h, 750 degree C-0.5 h/560 degree C-10 h, 750 degree C-0.5 h/C.R/560 degree-10 h respectively, and their microstructures were examined by transmission electron microscopy (TEM). Lastly, the corrosion characteristics were investigated with autoclave tests in 0.04 M LiOH aqueous solution at 350 degree C, 16.8 Mpa. It has been found that the corrosion resistance of specimens treated at 750 degree C-0.5 h/C.R/560 degree C-10 h is the best among all specimens treated in different ways in this work. It is concluded that a lower niobium concentration in solid solution in αZr matrix and a uniform distribution of nanoscale β Nb(containing iron) particles, especially the later one, are important factors for improving the corrosion resistance significantly. The cold deformation before the final annealing at 560 degree C plays an important role in obtaining nanoscale β Nb particles because it can promote the nucleation during the β Zr decomposition