Herein, the effect of Zn (2,3,4 and 5 wt%) addition on the microstructure, corrosion behavior, and biocompatibility of Mg‐xZn‐0.5Ca‐0.4Zr alloys is discussed by micromorphology, immersion/electrochemical, and cytotoxicity experiments. The results reveal that all as‐cast samples with a duplex morphology consist of Mg7Zn3 phase and α‐Mg matrix. With the addition of Zn element, the quantities of Mg7Zn3 phase increase gradually; while its micromorphology obviously changes from dot‐like to network shape, the average grain size decreases gradually. In addition, corrosion mechanism demonstrates that all as‐cast alloys suffer from microgalvanic corrosion between eutectic Mg7Zn3 and α‐Mg substrate due to potential difference of |ΔE| = 180 mV. However, the strip‐shape Mg7Zn3 contained in the Mg–4Zn–0.5Ca–0.4Zr alloy and compared with dot‐like\network shape phase can effectively hinder the spreading of corrosion from one grain to another, which causes Mg–4Zn–0.5Ca–0.4Zr to exhibit superior corrosion resistance. In addition, the biocompatibility conducted by methyl‐thiazolyl‐tetrazolium method via L929 cells reveals that as‐cast Mg–4Zn–0.5Ca–0.4Zr alloy is confirmed with low hemolysis rate (H% = 2.5%) and excellent proliferation capability (P% > 100%), which suggest that Mg–4Zn–0.5Ca–0.4Zr may be a good candidate for implant application.

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