A new magnesium alloy, named as Mg-6Zn-6Al(ZA66), using for thixoforming production has been developed. The microstructure of the material during partial remelting holding in the semi-solid state was characterized. The results indicate that non-dendrite microstructure in ZA66 magnesium alloy billets can be obtained, but the proper partial remelting temperature and holding time should be select. After being treated at 575°Cfor 20 min, the ZA66 alloys can obtain a non-dendritic microstructure with finer unmelted primary solid particles (37 μm) and shape factor about 0.6. With the increasing holding temperature from 575°C to 590°C,the average size of unmelted primary solid particles increases and globular tendency becomes more obvious.