The as-cast microstructures of Mg-5Sn-xGd（x=0

0.5

1.0

4.0

6.0） alloys have been observed.The experimental results indicate that with increasing in Gd content

the lamellar α-Mg+Mg2Sn eutectic phase which is mainly distributed continuously in the grain boundary areas of the alloy is reduced and becomes discontinuous.With 4% Gd addition

the eutectic phase in the alloy can be hardly found.In addition

a new fine Mg-Sn-Gd phase with irregular shape is generated in near grain boundary of the alloy with the decrease of eutectic phase

increased with increasing in Gd content.The DSC analysis indicate that the rare-earth phase has a phase transition at 582 ℃.The addition of Gd has an obvious effect on the distribution of the element Sn in the alloy.