To obtain lightweight multicomponent magnesium alloys with high tensile strength, ductility, and stiffness, two extruded Mg_92−5xAl_1.5+3xZn₃Cu_3.5+xCe_x (x=0.5 and 1, labeled as C0.5 and C1) alloys were designed. The results reveal that the ultimate tensile strength, yield strength (YS), and fracture strain of the C0.5 alloy are simultaneously improved compared to those of the C1 alloy, with values of 346 MPa, 312 MPa, and 11.7%, respectively. This enhancement is primarily attributed to the refinement of numerous secondary phases (micron scale Al₃CuCe, micron scale MgZnCu, and nanoscale MgZnCu phases). The calculation of YS shows that the Orowan strengthening and coefficient of thermal expansion mismatch strengthening are the main strengthening mechanisms, and the contribution values of both to the YS are 28 and 70 MPa for C0.5 alloy. In addition, the C0.5 alloy has a greater plasticity than the C1 alloy because the ác+añ slip system is initiated.