Tensile tests were performed on T4-treated specimens of GN62K (Mg-6Gd-2Nd-Zr(wt%)) and GN112K (Mg-11Gd-2Nd-Zr) alloys at room temperature and on T6-treated ones from room temperature to 300°C. The fracture behavior was investigated by using SEM images of fracture surfaces together with optical metallographs adjacent to the surface. Quasi-cleavage fracture was observed in the fracture surfaces of both alloys in T4-treated condition, and it seems that RE content has no significant effect on the fracture mechanism in T4-treated alloys. As for T6 treated condition, cracking was in a manner of transgranular cleavage and/or quasi-cleavage fracture in GN62K alloy but intergranular fracture in GN112K alloy, which implies that the fracture mechanism in T6-treated Mg-Gd-Nd-Zr alloys can be altered by the amount of RE addition. This phenomenon is interpreted in association with the relative strength of grain bulk and boundary.