Abstract: In this study, a bimodal structured Mg-4Li-3Al-1Sn (LAT431) alloy fabricated via extrusion and rotary swaging achieved a remarkable combination of high strength and high damping capacity. After rotary swaging, the alloy exhibited a yield strength of 305 MPa, an ultimate tensile strength of 387 MPa, and an elongation of 18.5%. Simultaneously, this mechanical enhancement coexisted with a high damping capacity, evidenced by a value of 0.02 at room temperature under a strain amplitude of ε = 10⁻³. The extruded alloy exhibited a bimodal structure consisting of a minority of fine grains (FGs) and a majority of coarse grains (CGs). Additionally, a substantial number of finely dispersed precipitates were observed within the matrix. After rotary swaging, the volume fraction of FGs increased significantly, and deformation twins formed within CGs. Furthermore, the density of precipitates increased while their average size decreased. Strain-induced segregation of Al atoms was also detected around Sn-rich precipitates. In the rotary swaged alloy, the formation of lamellar twins, the increase in mobile dislocations, and the redistribution of solute atoms collectively ensured that the high strength was accompanied by favorable damping performance. The attractive combination of damping capacity and mechanical properties offers new insights into the design of bimodal microstructures for developing high-performance Mg alloys.