The microstructure and mechanical properties of as-cast Mg–Ca–Y–Zr alloys with different Y contents were investigated. The alloy containing 0.5 wt% Y exhibited finer grains compared to the alloys with higher Y content. All alloys had a dendritic microstructure with eutectics composed of α-Mg and Ca-rich intermetallic phases. Few Mg–Y-rich intermetallic particles were also found along grain boundaries. EDS analysis showed that the solute Y segregated at dendritic and grain boundaries. The amount of Y contained in eutectics remarkably increased with increasing Y. In addition, the eutectics volume fractions of all alloys were comparable but the morphology became less continuous at higher Y contents. Both the room temperature tensile and compressive strengths were largely improved with increasing Y content. Moreover, the elevated temperature compression tests showed that the compressive yield strength first decreased slightly when the temperature rose to 175 °C, but then remained stable as the temperature increased.