Tri-layered Cu/Al-Mg-Si/Cu clad composite was cold roll-bonded, and its mechanical/electrical properties were studied. In the roll-bonded and aged Cu/Al-Mg-Si/Cu clad composite, neither interfacial reaction layer nor interface defects were observed. The strength as high as 415 MPa with the conductivity of 82 % IACS was attained in 3-ply lightweight Cu/Al-Mg-Si/Cu clad composite. The ductility and conductivity of clad composite are increased appreciably with heat treatment at 175 • C. After mechanical testing, the interface crack propagation and fracture in the well-bonded interface between metallic Cu and Al occurred in softer Al matrix. The increase of detached Al lumps onto the separated Cu side in clad composite heat-treated at 175 • C strongly supports that the interface bonding can be enhanced during aging of Al-Mg-Si alloy layer in Cu/Al-Mg-Si/Cu clad composite. The increased ductility in the aged Cu/Al-Mg-Si/Cu clad composite can be attributed to the enhanced interface bonding and precipitation in Al-Mg-Si layers.