Mg–Zn–Mn-based alloys have received considerable attention because of their high creep resistance, strength,and good corrosion resistance. The alloying element Mn in Mg–Zn-based alloys is commonly less than 1 wt%. In the present study, the effect of high Mn content(1 wt% and 2 wt%) on the microstructures and mechanical properties of Mg–2Zn–0.3Sr extruded alloy was investigated. The results revealed that the high Mn content significantly increased the ultimate tensile strength, tensile yield strength, compress yield strength, and yield asymmetry of the alloy without affecting its ductility. The dynamically recrystallized(DRXed) grains of Mg–2Zn–0.3Sr were remarkably refined because of the large amount of fine Mn precipitates in the homogenized alloy. The improved strengths were mainly attributed to the fine DRXed grains according to the Hall–Petch effect and to the large amount of spherical and < 0001 > Mn precipitates through the precipitation and dispersion strengthening. The fine DRXed grains and numerous Mn precipitates effectively suppressed the extension twining, substantially enhanced the compress yield strength, and resulted in improved anisotropy. Mg-Zn-Mn-based alloys have received received attention because of their high creep resistance, strength, and good corrosion resistance. The alloying element Mn in Mg-Zn-based alloys commonly has less than 1 wt% the effect of high Mn content (1 wt% and 2 wt%) on the microstructures and mechanical properties of Mg-2Zn-0.3Sr extruded alloy was investigated. The results revealed that the high Mn content significantly increased the ultimate tensile strength, tensile yield strength, compress yield strength, and yield asymmetry of the alloy without affecting its ductility. The dynamically recrystallized (DRXed) grains of Mg-2Zn-0.3Sr were remarkably refined because of the large amount of fine Mn precipitates in the homogenized alloy. strengths were mainly attributed to the fine DRXed grains according to the Hall-Petch effect and to the large amount of spherical and <0001> Mn precipitates through the precipitation and dispersion strengtheni ng. The fine DRXed grains and numerous precipitators effectively suppressed the extension twining, substantially enhanced the compress yield strength, and resulted in improved anisotropy.