In　this　study,　the　Mg-4Y-1Gd-1Nd-xCa-1Zn-0.3Zr　(x　=　0　and　0.4　wt%)　cast　alloys　with　low　rare　earth　concentration　were　prepared　in　different　routes　of　heat　treatments,　and　their　microstructures　and　mechanical　properties　were　investigated.　The　Mg-4Y-1Gd-1Nd-1Zn-0.4Ca-0.3Zr　cast　alloy　with　ultimate　tensile　strength　(UTS)　of　264　+/-　7.8　MPa,　tensile　yield　strength　(TYS)　of　153　+/-　1.2　MPa　and　elongation　to　failure　(EL)　of　17.2　+/-　1.2%　was　successfully　developed　by　appropriate　heat　treatment.　The　improved　mechanical　performance　was　attributed　to　the　combined　strengthening　effects　of　fine　grains,　-Mg24RE5,　beta＇,　beta(1),　gamma＇　and　LPSO　phases.　In　the　heat　treatment　process,　cooling　method　of　T4　treatment　affected　the　microstructure,　which　consequently　determined　the　mechanical　properties　air　cooling,　rather　than　water　cooling,　gave　rise　to　the　formation　of　gamma＇　phase　in　the　alloy　without　Ca　addition.　However,　Ca　addition　facilitated　the　formation　of　gamma＇　phase,　and　the　gamma＇　phase　precipitated　in　the　alloy　after　T4　treatment　either　by　water　cooling　or　by　air　cooling,　but　the　air　cooling　increased　the　number　density　of　gamma＇　phase　in　comparison　to　the　water　cooling.　Although　the　gamma＇　phase　strengthened　the　studied　alloys,　the　formation　of　gamma＇　phase　inhibited　the　precipitatition　of　beta＇　and　beta(1)　phases　in　the　following　T6　treatment,　and　consequently　reduced　the　strengthening　effect　of　beta＇　and　beta(1)　phases.　The　results　showed　that　the　mechanical　performance　of　the　studied　alloys　was　largely　determined　by　the　precipitation　of　gamma＇　phase,　which　was　regulated　by　the　Ca　addition　and　the　cooling　method　of　T4　treatment.