The microstructure evolution and oxide film behavior in ultrasound-assisted transient liquid phase(U-TLP) bonding of Mg alloy were investigated by applying different ultrasonic time at 460?C with brass interlayer in air. The results indicated that with increasing ultrasonic time, brass interlayer disappeared gradually and the Mg-Cu-Zn eutectic compounds were formed. The eutectic compounds in the joint decreased as the ultrasonic time increased further. The oxide removal process was divided into four steps. Continuous oxide film at the interface was partially fractured by ultrasonic vibration,and then suspended into liquid by undermining eutectic reaction. After that, the suspended oxide film was broken into small oxide fragments by ultrasonic cavitation effect, which was finally squeezed out of the joint by ultrasonic squeeze action. In addition, the mechanical properties of the joints were investigated. The maximum shear strength of the joint reached 105 MPa, which was 100% of base metal. The microstructure evolution and oxide film behavior in ultrasound-assisted transient liquid phase (U-TLP) bonding of Mg alloy were investigated by applying different ultrasonic time at 460? C with brass interlayer in air. The results indicated that with increasing ultrasonic time, brass The disappearance gradually and the Mg-Cu-Zn eutectic compounds were formed. The eutectic compounds in the joint decreased as the ultrasonic less increased further. The oxide removal process was divided into four steps. vibration, and then suspended into liquid by undermining eutectic reaction. After that, the suspended oxide film was broken into small oxide fragments by ultrasonic cavitation effect, which was finally squeezed out of the joint by ultrasonic squeeze action. the joints were investigated. The maximum shear strength of the joint reached 105 MPa, which was 100% of base me tal.