Abstract: In order to find the suitable etching agent for removing the surface oxidation film of ultrathin titanium foil before brazing, TA1 titanium foil with a thickness of 0.15 mm was acid pickled in HNO₃-HF-H₂O-based etching agent to investigate the influencing factors. The results show that the higher the content of HF, the greater its effect on the corrosion quantity and mechanical properties of the titanium foil. And the higher the HNO₃ content, the smaller its effect on the corrosion quantity and mechanical properties of the titanium foil. Therefore, increasing the content of HNO₃ corrosive agent can effectively reduce the effect of HF on the corrosion quantity and mechanical properties of the titanium foil. When pickling at room temperature, the corrosive composition has the most significant effect on the corrosion quantity and mechanical properties of the titanium foil. The pickling temperature and time has a great influence on the corrosion quantity and mechanical properties of the titanium foil as well. So the 35% HNO₃+3% HF+62% H₂O is suitable as a corrosive agent for removing the surface oxide film of the ultra thin titanium foil before brazing.