Abstract Half-metallic ferromagnets RuMn 2 Ge and RuMn 2 Sb have been studied in stable F-43m phase. The optimized equilibrium lattice constants in F-43m phase were found to be 5.90 A and 6.10 A for RuMn 2 Ge and RuMn 2 Sb, respectively. The materials exhibit half-metallic city with an energy gap in the spin-down channel of 0.38 eV for RuMn 2 Ge and 0.4 eV for RuMn 2 Sb. The calculated total magnetic moments of 2.0 μ B per unit cell for RuMn 2 Ge and 3.0 μ B per unit cell for RuMn 2 Sb are in good agreement with Slater–Pauling rule. The magnetic moments of Mn-I and Mn-II mainly contribute to the total magnetic moment of the materials and are antiparallel to each other, hence predicting the signature of ferrimagnetism in RuMn 2 Z alloys. The shifting of bands towards lower energies in spin-down channel for RuMn 2 Sb may be due to the strong covalent character of bonding than RuMn 2 Ge.