Mg-Zn-Mn alloy ZM71 with different additions of Ce element was hot extruded and then was heat-treated. Tensile mechanical properties at room temperature of different states ZM71 and ZM71-xCe alloys were also tested. Microstructure observations under different states were performed by means of optical microscopy (OM), X-ray diffraction analysis (XRD), Scanning electron microscopy (SEM), differential thermal analysis (DSC), energy spectrum analysis (EDS), and transmission electron microscopy (TEM). The existence form and acting mechanism of Ce elements in ZM71 alloy and the influence of Ce content on microstructure and mechanical properties of ZM71 alloy were investigated. The results show that a ternary τ phase was identified in ZM71-xCe alloys, which distributed at grain boundaries and interdendritic, and refined the microstructure of as-cast alloys. Ce element had an obvious effect on refining the microstructure of as-extruded alloys by restricting the occurrence of dynamic recrystallization and restraining the grain growth during extrusion and improved the mechanical properties, but the Ce addition should be no more than 1%. ZM71-0.5Ce alloy had better overall mechanical properties, with σb =318 MPa, σ0.2=250 MPa and δ=13.6%. Solution and aging was not available for improving mechanical properties of as-extruded Mg-Zn-Mn-Ce with high Zn content