In　this　work,　we　distinctly　emphasize　the　critical　roles　of　morphologies　of　second　phases　in　determining　corrosion　behaviors　in　biodegradable　Mg-xZn-0.2Mn-0.2Ca　(MX-xZn,　x　=　1,　2,　3　and　4,　wt%)　alloys.　We　found　that　spherical-shaped　Ca2Mg6Zn3　phases　in　MX-1Zn　alloys,　with　their　higher　Volta　potential,　initially　caused　shallow　pits　formation　by　preferentially　corroding　and　detaching　from　the　matrix.　Conversely,　island-shaped　Ca2Mg6Zn3　phases　in　other　alloys　accelerated　corrosion　rates　significantly　by　forming　corrosion　channels,　leading　to　extensive　pits　formation　along　grain　boundaries　over　prolonged　immersion　periods.　Prolonged　immersion　tests　(14　days)　demonstrated　that　these　grain　boundary　networks　underwent　severe　structural　degradation,　ultimately　leading　to　phase　detachment　and　the　creation　of　deep　corrosion　cavities　at　boundary　regions.　The　descending　order　of　corrosion　resistance　was　quantitatively　established　as:　MX-1Zn　＞　MX-2Zn　＞　MX-3Zn　＞　MX-4Zn.　The　in　vivo　biocompatibility　assessments　confirmed　that　MX-1Zn　alloy　implants　exhibited　no　adverse　histological　effects　on　hepatic　and　renal　tissues　in　animal　models.