First-principles calculations based on density functional theory (DFT) for RbSrX 2 (X = C, N, and O) Heusler compounds were performed using the selfconsistent full-potential linearized augmented plane wave (FPLAPW) method. The results showed that the ground state of all three compounds in ferromagnetic state was the AlCu 2 Mn-type structure. The RbSrC 2 in the AlCu 2 Mntype and CuHg 2 Ti-type structures was a nonmagnetic metal, while RbSrN 2 and RbSrO 2 compounds in both structures were half-metallic ferromagnets. The calculated majority band gaps for RbSrN 2 and RbSrO 2 compounds in the AlCu 2 Mn-type (CuHg 2 Ti-type) structure were 5.3 (2.7) and 4.7 (3.4) eV, respectively. The origin of majority band gaps was also studied using the band structure calculations and density of states (DOSs). The total magnetic moment of RbSrN 2 and RbSrO 2 compounds were respectively obtained 3 and 1 μ B per formula unit at the equilibrium lattice parameter, which were in agreement with Slater-Pauling rule (M tot = 12 − Z tot ). The RbSrN 2 and RbSrO 2 compounds respectively maintained their half-metallic characteristic at lattice constants ranges of 5.71-8.82Å (5.73-8.36Å) and 5.64-8.93Å (5.13-8.05Å) for AlCu 2 Mn-type (CuHg 2 Titype) structure, indicating that the lattice distortion did not affect the half-metallic properties of the compounds, which makes them interesting materials in the spintronic field.