Abstract: To achieve reliable bonding between AZ31B magnesium alloy and copper, diffusion bonding tests for AZ31B magesium alloy and Cu with Al interlayer were carried out at 450 ℃ for 30-120 min, and the effects of holding time on microstructure, microhardness and shear strength of the joint were studied. The results show that the transient liquid phase bonding for the joint could not be achieved when holding time was 30 min. When holding time was 60 min, Al interlayer completely dissolved, and a diffusion zone with width about 150 μm formed in the joint, the microstructures of diffusion zone were magnesium-based solid solution, eutectic structure and Cu3Al2Mg2 intermetallic compound, in turn, from magnesium alloy side to Cu side. After holding for different times, microhardness increased in a stepped form from magnesium alloy side to Cu side in diffussion zone. With the increase of holding time, microhardness of Cu side in fussion zone increased remarkably, shear strength of the joint increased firstly and then decreased, and up to the maximun value of 68.2 MPa when holding time was 90 min. Fracture occurred at diffusion zone near Cu side.