Abstract <p>This research investigates the effect of manganese (Mn) content on the microstructure, mechanical, and corrosion properties of a Mg–1Zn–0.3Ca–0.3Sr cast alloy. For this purpose, Mg–1Zn–0.3Ca–0.3Sr alloy that contained 0, 0.2, 0.4, 0.6 wt pct manganese, was cast and prepared. Both optical and scanning electron microscopes were used to investigate the microstructure, and also mechanical properties were examined and evaluated using tensile and hardness tests. X-ray diffraction analysis was also employed to identify the phases in the structure. The corrosion properties were evaluated using potentiodynamic polarization (PDP) and corrosion tests in simulated body fluid (SBF). As manganese content increased, the average grain size decreased from 133 to 115, 102 and 76 <i>μ</i>m, respectively. The addition of manganese (0.6 wt pct Mn) raised hardness of the alloy (from 36.6 to 41.6 HV). Tensile test results showed that the strength values have improved by increasing manganese content up to 0.2 pct and then decreased in higher amounts of manganese, therefore the tensile strength of the alloy has raised from 143 to 176 MPa by increasing manganese content from 0 to 0.2 pct. The results of corrosion tests showed the improvement of alloy properties by adding manganese, and the best properties are reported in 0.6 wt pct Mn alloys. Therefore, Mg–1Zn–0.3Ca–0.3Sr–0.6Mn alloy can be selected as a candidate to be used as a biodegradable alloy. Fracture results showed that the failure mechanism of the cast alloys was mainly a combination of brittle and ductile fracture.</p> Graphical Abstract <p></p>