Static annealing process of 423 K for 2.5 h is adequate to segregate alloying elements at {101¯2} twin boundaries in various Mg binary alloys. These segregated twin boundaries play a role in obstruction of dislocation slips; thus, they contribute to increase in hardness. Internal friction tests reveal that, irrespective of the solute elements, induced twin boundaries are effective in enhancing damping capacity, owing to their reversible motion, i.e., growth and shrinkage. In contrast, by comparison of the loss factor of specimens with/without twin boundary segregation, segregation leads to a decrease in damping capacity. The energy barrier required for twin boundary sliding to occur is closely related to the loss factor. When solute element having a characteristic of high (or low) energy barrier exists at twin boundaries, such an alloying element prevents (or enhances) the occurrence of twin boundary motion; as a result, shows a low (or high) loss factor. Display omitted