In　this　study,　we　investigated　the　effects　of　single-stage　ageing　(SSA),　two-stage　ageing　(TSA),　2%　pre-strain　+　single-stage　ageing　(P2%SSA)　and　2%　pre-strain　+　two-stage　ageing　(P2%TSA)　on　the　mechanical　properties　of　as-extruded　Mg-8Gd-3Y-0.5Ag-0.5Zr　alloy　(E　alloy).　Compared　with　the　SSA　treatment,　the　TSA　treatment　increased　the　number　density　of　beta＇　phase.　The　P2%SSA　and　P2%TSA　treatments　generated　the　gamma＇　phase　and　chain-like　precipitates　in　addition　to　the　beta＇　phase.　The　contributions　of　these　ageing　treatments　to　the　alloy　strengthening　can　be　ranked　as　P2%TSA　＞　P2%SSA　＞　TSA　＞　SSA,　because　the　increments　in　the　tensile　yield　strength　were　estimated　to　be　199　MPa　＞　148　MPa　＞　144　MPa　＞　110　MPa.　Different　from　the　traditional　strengthening　of　beta＇　phase　in　the　E　+　SSA　and　E　+　TSA　alloys,　the　composite　precipitates　comprising　the　beta＇　phase,　gamma＇　phase　and　chain-like　precipitates　in　the　E　+　P2%SSA　and　E　+　P2%TSA　alloys　provided　better　combined　strengthening　effect.　The　beta＇　phase　was　still　dominated　in　the　strengthening　effect　of　the　composite　precipitates.　Owing　to　the　higher　number　density　of　beta＇　phase　in　the　composite　precipitates,　the　E　+　P2%TSA　alloy　exhibited　the　better　mechanical　performance　as　compared　with　the　E　+　P2%SSA　alloy.　Finally,　the　E　+　P2%TSA　alloy　had　the　ultimate　tensile　strength　of　452　MPa,　the　tensile　yield　strength　of　401　MPa　and　elongation　to　failure　of　3.3%.