Microstructures and mechanical properties of AZ61 with Cu addition are investigated by optical microscope（OM），X-ray diffraction analysis（XRD），differential thermal analysis（DSC），scanning electron microscopy(SEM) and energy spectrum analysis（EDS）.The results show that some ternary AlCuMg phases are observed along the grain boundaries and between dendrites in AZ61-xCu alloys, and they can refine the microstructure of as-cast alloys. Meanwhile, with the addition of Cu，the quantity and the size of β-Mg17Al12 decrease. As Cu content increasing, the strength of as-extruded alloys increase first and then decrease.The elongation has no obvious decrease until Cu content reaches 1.5%. AZ61-1Cu alloy has optimum combination mechanical properties,with σ0.2=230 MPa,σb=321 MPa and δ=9.7%,respectively.When Cu content is 1.5%, the coarse AlCuMg phase splits the matrix and deteriorates mechanical properties.