The effect of extrusion temperatures on the microstructures and mechanical properties of Mg-3Zn-2.5Al-2.5Ca(ZAC333) alloy was investigated by metallograph,SEM,XRD and tensile tests.The results show that the average grain size of the as-cast alloy is 185 μm. Due to the dynamic recrystallization,the grain size of as-extruded alloys was reduced from 6.32 μm to 3.36 μm with the extrusion temperature decreasing from 623 K to 523 K.The second phase of semi-continuous Al2Ca and continuous Ca2Mg6Zn3 was broken,which distributed along the grain boundary in the as-cast ZAC333 alloy. Compared with as-cast alloy,the mechanical properties of as-extruded ZAC333 alloy were improved. The tensile and yield strength of as-extruded alloy increased from 176 to 292 MPa,264 to 334 MPa,respectively,while elongation decreased from 20% to 9%. The improvement of mechanical properties for ZAC333 alloy can be attributed to the couple effects of refined crystalline strengthening caused by dynamic recrystallization and dispersion strengthening for the refined second phases during hot extrusion.