In this work, the effects of adding trace Sr elements on microstructure, mechanical properties and corrosion properties of Mg-0.2Zn-0.1Mn-xSr(x=0, 0.1, 0.2, 0.3 wt. %) alloys were investigated. The result of microstructure observation reveal that the grain size of the alloy decreases with the increase of Sr. The granular Mg17Sr2 phase is uniformly dispersed in the magnesium matrix. While, the second phase grows up as the Sr increases. The result of mechanical properties investigated by tensile test at room temperature indicated that micro Sr can improve the yield strength and tensile strength. But the elogations decreased with the increase of Sr. Degradation was studied using immersion tests in Kokubo solution. The corrosion rates were faster and the pitting was more likely to occur when the Sr increased. The average corrosion rates of Mg-0.2Zn-0.1Mn-xSr(x=0, 0.1, 0.2, 0.3 wt. %) that measured by weight loss were 6.85→6.01→6.80→7.52mm/a. Trace Sr can improve the corrosion resistance of magnesium alloys. However, with the increase of Sr content, the magnesium alloys are more prone to pitting and intergranular corrosion, which in turn reduces the corrosion resistance of magnesium alloys. The bio-corrosion behaviors can be attributed to the grain refinement and the diffused second phase, which can promote the formation of corrosion product film. However, the bigger second phase in the matrix will accelerate the local corrosion，which will reduce the corrosion resistance of magnesium alloy. The results show that Mg-0.2Zn-0.1Mn-0.1Sr has the best mechanical properties and corrosion resistance.