As an inevitable step during ultrasonic bonding of aluminum or copper materials, the removal of oxides that prevent the bond formation is essential for obtaining high quality. Nevertheless, the oxides removal process is still unclear after tens of years' application of ultrasonic bonding. In this project, the removal mechanism was investigated via the analysis of an artificially coated oxide layer. The oxide removal process was observed in real-time by a high-speed observation system and the oxides distribution after the bonding process was observed under an electron microscope. The results show that during the bonding process, the detached oxides first agglomerate into larger particles and were then pressed outside of the contact area. The areas of the particles were counted and fit to a lognormal distribution.