As-cast AM50 magnesium alloys containing 0, 1, 2 wt. %Ca were extruded firstly at 673K with an extrusion ratio 1:9, and then at 573K with an extrusion ratio 1:16. Microstructure, tensile properties and fractographs were investigated. With Ca content increasing, the amount of Al2Ca increases and that of Mg17Al12 decreases. Ca refines the microstructure of as-cast and extruded AM50 magnesium alloys. For the extruded magnesium alloys, tensile strength improved and elongation decreased at room temperature, while tensile strength was reduced a little and elongation reduced at the temperature of 100°C, 150°C and 200°C with increasing Ca content. The tearing face increases with Ca content increasing for the tensile fractographs.