The present invention is a biodegradable magnesium alloy composed of x weight% of calcium, y weight% of zinc, balance of magnesium and unavoidable impurities, and x and y are represented by the following formula (1) (y = 44.894 × 2-25.123 × 5. 192) and the upper part of the trajectory according to Equation 2 (y = -10.618x2 + 7.8784x + 0.1637) have a range corresponding to a region where they overlap each other on the xy plane, and the zinc compound phase is a zinc compound phase. When the total weight of the phase is 90% by weight or more, it is characterized by containing Ca2Mg6Zn3.本発明は、ｘ重量％のカルシウム、ｙ重量％の亜鉛、残部のマグネシウム及び不可避不純物からなる生体分解性マグネシウム合金であり、ｘとｙは、数式１（ｙ＝４４．８９４ｘ２－２５．１２３ｘ＋５．１９２）による軌跡の下部と数式２（ｙ＝－１０．６１８ｘ２＋７．８７８４ｘ＋０．１６３７）による軌跡の上部とがｘｙ平面で互いに重畳される領域に該当する範囲を有し、亜鉛化合物相は、亜鉛化合物相を全体重量とするとき、９０重量％以上のＣａ２Ｍｇ６Ｚｎ３を含むことを特徴とする。
