This paper reports the investigation results on directional growth of Al-Mg_2Si eutecticalloy in the SZ2 unmanned spaceship.The analysis shows that microgravity has influence on thedirectional growth of Al-Mg_2Si eutectic alloy.The eutectic colony in space-grown sample is largerthan that in ground-grown sample,and the directional effect is not so good as that of terrestrialsample.But there is no obvious difference in the lamellar thickness between these samples,andlamellar interspacing in space sample is smaller than that grown on the ground.A simple discus-sion is done on the gravity effect on the directional growth of Al-Mg_2Si eutectic alloy. This paper reports the investigation results on directional growth of Al-Mg_2Si eutecticalloy in the SZ2 unmanned spaceship. The analysis shows that microgravity has influence on the directional growth of Al-Mg_2Si eutectic alloy. The eutectic colony in space-grown sample is largerthan that in ground. -grown sample, and the directional effect is not so good as that of terrestrials sample.But there is no obvious difference in the lamellar thickness between these samples, andlamellar interspacing in space sample is smaller than that grown on the ground. A simple discus-sion is done on the gravity effect on the directional growth of Al-Mg_2Si eutectic alloy.