Two　duplex　Mg-Li　alloys,　Mg-8.02Li-0.210Y　and　Mg-8.43Li-0.353Ymm　(Y-rich　mischmetal)　alloys,　were　prepared　by　casting　method　with　a　permanent　metal　model.　Microstructures,　mechanical　properties　and　deformation　behaviors　at　tensile　rates　from　1.28　x　10(-4)　s(-1)　to　1.28　x　10(-3)　s(-1)　were　evaluated.　The　results　showed　that　when　increasing　the　tensile　speed,　the　strength　increased　with　a　decreasing　elongation.　The　strength　and　ductility　of　Mg-8.02Li-0.210Y　alloy　were　more　sensitive　to　the　tensile　speed.　Fracture　occurred　mainly　in　the　beta-Li　phase,　and　the　alpha-Mg　phase　participated　into　fracture　at　relatively　high　tensile　speeds,　which　led　to　the　strength　increase　of　both　alloys　with　the　increment　of　tensile　speed.　Long-stripe-like　alpha-Mg　grains　in　Mg-8.02Li-0.210Y　alloy　hindered　the　fracture　and　resulted　in　a　higher　elongation.　Mg-8.02Li-0.210Y　alloy　presented　a　serrated　effect　at　a　relatively　high　initial　rate　of　1.28　x　10(-3)　s(-1).　This　was　proposed　to　be　resulted　from　the　interaction　between　slips　and　alpha-Mg　grains,　whichwas　quite　different　from　the　serrated　effect　explained　by　the　dynamic　strain　aging　(DSA)　mechanism.　(C)　2015　Elsevier　Ltd.　All　rights　reserved.