The corrosion behaviour of Zr—1% Nb is studied after ultrasonic impact treatment (UIT). As shown using X-ray diffraction analysis and transmission electron microscopy, the significant refinement of a grain structure (up to $\cong$ 100—150 nm) and the reinforcement in the basal texture occur in the surface layer with increasing deformation during the UIT process. Compressive residual stresses (up to 550 MPa) are also registered in the surface layer at UIT. These structural factors lead to an increase in the microhardness of the surface layer up to 2.9 GPa. As shown using energy dispersive X-ray analysis, the degree of oxygen saturation into the surface layer at UIT and strength of oxide films formed in the NaCl solution depend on the environment used at the UIT processing (air or argon). Higher oxygen saturation into the surface layer at the air UIT process promotes formation of thicker ZrO$_{2}$ oxide films on the specimen surface. Corrosion tests in 3.5% NaCl water solution with using open circuit potential and dynamically changed potential schemes show a determining role of the oxide passivation film in the enhanced corrosion resistance of Zr—1% Nb alloy.