Copper（T2） and aluminium alloy（5 A06） were welded by friction stir welding（FSW）.The microstructure,mechanical properties and fracture characterization of FSW joints were studied by metallography,tensile testing machine and scanning electron microscope（SEM）.The results indicated that the high quality weld joint could be obtained when tool rotational speed was 950 r/min,and travel speed was 150 mm/min.The maximum value of tensile strength was about 296 MPa.The metal Cu and Al close to copper side in the weld nugget（WN） zone showed a lamellar alternating structure characteristic.However,a mixed structure characteristic of Cu and Al existed in the aluminium side of weld nugget（WN） zone.Macroscopic fracture surfaces of the weld section showed obvious layered characteristic,and there were a lot of dimple structures of ductile fracture character in the middle layer of the fracture.The brittle Al-Cu-Mg intermetallic compounds of brittleness were found in the dimple.