Abstract: The effects of pouring temperature, holding time and rare earth La content on the microstructure of AZ61 magnesium alloy were investigated by OM, SEM. The results indicate that with increasing pouring temperature, the microstructure of the alloy was more uniform, grains grew up and became more rounding and coarser in the mean time. The most uniform microstructure with the most rounding grains was obtained when pouring temperature was 720 ℃. There were no obvious influences of holding time on the microstructure of the alloy. With the increase of rare earth content, dendritic primary phase of α-Mg was refined and the rare earth phase began to grow. When the rare earth content was 1.0wt.%, β-Mg17Al12 phases uniformly distributed around grain boundaries, the uniform distribution of rare earth phase was observed and no agglomeration of rare earth phase was found.