Influences of Ca addition on microstructures and mechanical properties at room and elevated temperatures up to 300oC have been investigated for EZ43 (Mg-4%RE-3%Zn)-(0~1.2)%Ca permanent mould casting alloys, based on experimental results from optical micrography, X-ray diffractometry, scanning electron microscopy combined with energy dispersive X-ray spectroscopy and mechanical tests. With an increase in Ca content, yield strength is increased gradually at all temperatures, whereas elongation shows a decreasing tendency. High level of tensile strength around 150MPa is maintained until 250oC in the EZ43-0.8Ca and EZ43-1.2Ca alloys, meaning that Ca is very effective for improving elevated temperature strength of the Mg-RE-Zn alloy. The microstructural examinations reveal that Ca refines the a grains markedly, increases discontinuity of Mg12RE network intermetallic compound and dissolves into the Mg12RE phase. The refined a grains and Ca-containing Mg12RE with higher thermal stability are considered to be responsible for the improved mechanical properties at room and elevated temperatures for the EZ43-Ca alloys.