The ultrasonically brazing of 55 vol.% SiCp/A356 composites in air has been investigated. When the ultrasonic vibration is applied for 0.5s, the oxide layer is still continuous at most places between the filler metal and the composites. The shear strength is only ~30% of that of the base composites. As the ultrasonic action time increases, the oxide film sufficiently disappears in the bond region, and the wetted area between the filler metal and SiC particles increases gradually. As a consequence of this, the shear strength of bonds also increases with the ultrasonically acting time. The maximum value of the shear strength of the bonds reaches 165.5MPa when the ultrasonic acting time increases to 5s, which is similar to the shear strength of the base composites.