The　Mg　matrix　composite　(Mg(2)Si/Mg-5Zn-2.5Er)　was　prepared　using　repeated　plastic　working　(RPW)　technique.　and　the　effects　of　the　number　of　RPW　cycles　on　the　microstructure　and　mechanical　properties　of　these　composites　were　investigated.　The　results　indicated　that　the　added　silicon　particles　fully　reacted　with　the　magnesium　matrix,　and　theMg(2)Si/Mg-5Zn-2.5Er　composites　were　successfully　achieved.　When　the　number　of　RPW　cycle　increased,　the　size　of　the　Mg(2)Si　particles　decreased,　and　the　grain　size　of　the　matrix　alloy　reached　the　minimum　when　200　RPW　cycles　was　used.　The　best　mechanical　properties　were　also　identified　as　394　MPa　ultimate　strength,　and　363　MPa　yield　strength,　when　200　RPW　cycles　were　used.