The microstructure and corrosion resistance of Mg-6Zn-4Si alloy with Sr addition were studied using XRD, OM, SEM, EDS, potentiodynamic polarization and immersion testing. A proper Sr addition observably modifies the morphologies and sizes of primary and eutectic Mg2Si phases in Mg-6Zn-4Si alloy. The grain size of the primary Mg2Si decreased initially and then gradually increased with the increasing of Sr amount. Sr significantly improves the corrosion resistance of Mg-6Zn-4Si alloy. The ternary alloy with 0.5Sr has the optimal corrosion resistance, which exhibits the highest corrosion potential, the lowest corrosion current density and corrosion rate. The homogeneous dispersion of fine Mg2Si particles with Sr element is responsible for the improvement of corrosion resistance. Excessive Sr (≥1.0%) leads to the generation of SrMgSi new phase, which has unfavorable effects on the corrosion resistance of the alloys.