Effects of trace element Sr on the as-cast microstructure and mechanical properties of magnesium alloy AM60B were studied by optical microscope (OM), field emission scanning electron microscopy (FESEM), electronic universal testing machine, digital display Rockwell hardness tester and microhardness tester. The results show that the addition of trace element Sr can refine grains without change of dendrite morphology of matrix α-Mg phase, but can change the morphology and size of γ-Mg17A112 phase from continuous/discontinuous netlike or strip form to cobble or particulate form. The effect of Sr on the tensile strength and elongation of AM60B magnesium alloy has the similar tendency, i.e. with the increase of Sr content, the tensile strength and elongation of AM60B magnesium alloy are first increased and then decreased. With addition of 0.05% Sr, the tensile strength and elongation reach the maximum 191.82 MPa and 4.63%, respectively, while the Rockwell hardness and microhardness are increased with the increase of Sr content. The fracture mechanism of AM60B magnesium alloy is changed from cleavage fracture to quasi-cleavage fracture to cleavage fracture