Abstract: The effect of Sr addition on the grain refinement of ZK60 magnesium alloy was investigated by means of OM, SEM and EDX. The results indicate that adding small amounts of Sr can effectively refine the as-cast microstructure of ZK60 alloy, but the effects of Sr adding amount and melt holding time on the refinement efficiency are obvious. For a given melt holding time, the refine-ment efficiency enhances with the Sr adding amount increasing from 0.01% to 0.1%. For a given Sr adding amount, the refinement efficiency enhances with the melt holding time increasing from 20 to 80 min, hut reduces obviously while the melt holding time exceeds 80 min.