Hot tearing susceptibility of Mg-Gd alloys are investigated using instrumented constrained rod casting (CRC) apparatus, and found that the susceptibility increases with increase in Gd content, and reaches a maximum at 2 % after which it decreases to a minimum with 10 % Gd. The high susceptibility observed with 2 % Gd is due to its columnar structure and low amount of eutectic liquid at the time of cracking, whereas equiaxed grain and high liquid content which facilitates crack healing are the reasons for the low susceptibility of Mg-10 Gd alloy.