The effects of Ca addition on microstructure and mechanical properties of ZA104 permanent moulding magnesium alloy were investigated. The results indicate that micro-alloying element Ca is involved in the formation of strengthening phases in ZA104 tested alloy. With increase of Ca content, discontinuous or semi-continuous lamellar and fine lattice microstructures evolve into coarse, continuous and bone-like network gradually. Strengthening phases change from τ and φ phases into τ1 and τ2 phases by degrees. Brinell hardness of the alloy is increased linearly. And it increases sharply when Ca content is lower than 0.3%, while increases slightly with further increase of Ca addition. Ca addition effectively improves high-temperature tensile strength by solid solution and participation in formation of high-temperature strengthening phase. When 0.3%Ca is added, both the room temperature and elevated temperature tensile strengths of the tested alloy reach the peak, which are 203 and 190 MPa, respectively. Meanwhile, the maximum of elongation –17.3% is obtained.