Abstract: This work studied the effects of adding Zr and Mn in amounts less than 1wt% on the microstructure, mechanical properties, casting properties, and corrosion resistance of Mg–Zn–Cu alloys containing 2.5wt% Cu and 2.5wt%–6.5wt% Zn. The hardness and electrical conductivity measurements were used to find an optimal heat treatment schedule with the best mechanical properties. It has been established that Zr significantly increases the yield strength of the alloys due to a strong grain refinement effect. However, the presence of Mn and Zr has a detrimental effect on alloy’s elongation at fracture. It was shown that the precipitation of the Mg₂Cu cathodic phase in the alloy structure negatively affects the corrosion behavior. Nevertheless, the addition of Mn decreases the corrosion rate of the investigated alloys. The best combination of the mechanical, casting, and corrosion properties were achieved in the alloys containing 2.5wt% Cu and 5wt% Zn. However, the Mn or Zr addition can improve the properties of the alloys; for example, the addition of Mn or Zr increases the fluidity of the alloys.