Rolled Mg-Al-Sn series alloys generally possess limited formability due to the formation of strong basal texture. Texture weakening is an effective way to enhance formability, but usually accompanied with decreasing strength. In this work, synergistic enhancement of strength and formability is achieved in a Mg-3Al-1Sn-0.5Ca-0.1Sm (ATXS3110) alloy by 0.2 wt.% Mn addition combined with high temperature rolling, exhibiting a high index Erichsen (I.E.) value of ∼8.1 mm and near-isotropic mechanical properties. On one hand, after Mn addition, the grain refinement from ∼7.6 µm to ∼4.1 µm results in suppression of extension twinning, thereby preventing the development of strong basal texture upon stretch forming. On the other hand, trace Mn addition narrows the grain size distribution and promotes the formation of uniform fine grains, which induces homogeneous deformation during stretch forming. Moreover, grain refinement and high-density nano-sized precipitates caused by trace Mn addition increase the strength. This work may provide insights into designing low-cost Mg-Al-Sn series alloys with superior comprehensive mechanical properties for further structural applications.