Nickel was successfully introduced into the Gd 5 Sb 3 and Gd 5 Bi 3 binaries to yield the Gd 5 Ni 0.96(1) Sb 2.04(1) and Gd 5 Ni 0.71(1) Bi 2.29(1) phases. Both Ni-substituted compounds adopt the orthorhombic Yb 5 Sb 3 -type structure. While the Gd 5 Ni 0.71 Bi 2.29 phase is thermodynamically stable at 800 1C and decomposes at lower temperatures upon annealing, it can be easily quenched to room temperature by rapid cooling from 800 1C. The Gd 5 Ni 0.96 Sb 2.04 phase is found to be thermodynamically stable till room temperature. Through annealing at different temperatures, Gd 5 Bi 3 was proven to undergo the Mn 5 Si 3 -type (LT)2Yb 5 Sb 3 -type (HT) transformation reversibly, whereas Gd 5 Sb 3 was found to adopt only the hexagonal Mn 5 Si 3 -type structure. Orthorhombic Gd 5 Ni 0.96 Sb 2.04 and Gd 5 Ni 0.71 Bi 2.29 and low-temperature hexagonal Gd 5 Bi 3 order ferromagnetically at 115, 162 and 112 K, respectively. In Gd 5 Bi 3 , the ferromagnetic ordering is followed by spin reorientation below 64 K. Magnetocaloric effect in terms of DS was evaluated from the magnetization data and found to reach the maximum values of ร7.7 J/kgK for Gd 5 Ni 0.96 Sb 2.04 and ร5.6 J/kgK for Gd 5 Ni 0.71 Bi 2.29 around their Curie temperatures.