The magnetic properties of Sm 2 Fe 1 7 - x Ga x (x=0, 1, 2, 3) compounds and their hydrides are systematically investigated. The results reveal that all compounds have the Th 2 Zn 1 7 -type structure. As the content of Ga increases, the Curie temperature of Sm 2 (Fe,Ga) 1 7 compounds increases, and their saturation magnetization decreases.It was first discovered that Curie temperatures of the hydrides of Sm 2 (Fe,Ga) 1 7 compounds measured from the heating process are higher than that measured from the cooling process. The difference was denoted as ΔT c *. The correlation between ΔT c * and the structural stability of Sm 2 (Fe,Ga) 1 7 compounds as well as their corresponding hydrides was discussed.