A Ca-P coating consisting of biodegradable β-tricalcium phosphate [β-TCP, β-Ca3(PO4)2] accepted for medical application was coated on a biodegradable AZ31 alloy by chemical deposition to improve the corrosion resistance. The good bonding strength of the coating is obtained. The results show that the corrosion potential of the Ca-P coated AZ31 alloy increases significantly, and MG63 cells show good adherence, proliferation and differentiation on the surface of the coated alloy. The Ca-P coating might be an effective way to improve the surface bioactivity of magnesium alloys.