As-cast　Mg-Zn-Mn-Ca　alloys　are　the　candidates　for　medical　implants.　The　microstructure　and　mechanical　properties　of　the　as-cast　Mg-Zn-Mn-Ca　alloys　were　investigated　by　using　optical　microscope　(OM),　X-ray　diffraction　(XRD)　and　scanning　electron　microscope　(SEM).　The　results　suggested　that　the　addition　of　Zn　significantly　refined　the　grain　size　of　the　as-cast　magnesium　alloys,　and　hence　improved　the　mechanical　properties　of　the　alloys.　Meanwhile,　the　secondary　phase　mainly　distributed　in　the　grain　boundaries　and　the　solution　treatment　made　parts　of　secondary　phases　dissolved　into　the　matrix,　resulting　in　enhancement　of　the　plasticity　of　the　as-cast　Mg-Zn-Mn-Ca　alloy.