The corrosion kinetics of Zr–2.5Nb and Zircaloy-4 were studied at a temperature of 623 K in lithiated heavy water. The oxide films grown on both alloys during this exposure were strongly textured. The orientation distribution functions (ODF), calculated from the pole figures, showed that the major orientation components of the oxide formed on Zr–2.5Nb were (103̄)[01̄0] and (104̄)[401] while a (104̄) fiber texture was formed on Zircaloy-4. The transformation of the structure of the oxide films from the tetragonal to monoclinic phase was followed and the volume fraction changes of these two phases were estimated. The volume fraction of the tetragonal oxide phase decreased with an increasing exposure time in the oxide films of both materials and at the same time, a significant difference in oxidation kinetics of Zr–2.5Nb and Zircaloy-4 was recorded. The results suggest that Zircaloy-4 has a greater fraction of tetragonal phase and a better corrosion resistance than Zr–2.5Nb.