Mg-9Li-0.5Ca alloy with an eutectic structure was prepared by alloying Mg-9Li alloys with 0.5 wt.% Ca element and employing the magnetic levitation melting and copper mould suction casting method. Microstructure observation results show that ?-Mg phase in the conventional Mg-9Li alloy are coarse plates, oriented randomly and distributed homogeneously in the ?-Li matrix. While a eutectic structure consisting of alternating lamellae of ?-Mg and ?-Li phases was formed in Mg-9Li-0.5Ca alloy, which exists as grains, i.e. eutectic colonies. Within each colony ?-Mg phase are present in the form of long fibers (the length-to-diameter ratio of ~100) and such lamellae are oriented in essentially the specific direction. Also, large amounts of nano- or ultrafine-scale Mg2Ca particles are dispersed uniformly in ?-Mg and ?-Li grains and the ?-Mg/?-Li phase interface. As a consequence, Mg-9Li-0.5Ca alloy with such eutectic structure exhibits a significantly enhanced mechanical property with the yield strength increased by 3%, the tensile strength by 3.5% and the percent elongation by 50% compared to Mg-9Li alloy. It was inferred that small amount of Ca addition and a relatively fast cooling rate from the copper mould suction casting result in the formation of fine（?-Mg ?-Li）eutectic structure which greatly improves the mechanical property of Mg-9Li-0.5Ca alloy.