The electronic structures of the Fe-doped perovskite ruthenates BaRu1−x Fe x O3 with x = 0, 0.25, 0.5, 0.625, 0.75, and 1 are investigated through density-functional calculations. Large exchange splitting and small crystal field splitting are found in BaFeO3, and a contrary scenario can take place on BaRuO3 as expected since the Ru atom has a highly extended 4d orbital. The small exchange splitting and extended 4d states are the reasons why the obtained spin magnetic moment (0.628μ B ) is significantly lower than the spin only value (2μ B ) for the t 2g 3↑ t 2g 1↓ electronic configuration for Ru4+ ion. Further investigations suggest that Fe substitution at the Ru sites can suppress the bandwidths of Ru 4d orbital, leading to the half-metallic behaviour in BaRu1−x Fe x O3 with x = 0.625 and 0.75. The different orbital feature of the Ru4+ ions in BaRu0.375Fe0.625O3 is presented, which reflects the influence of Fe dopant on Ru 4d orbitals.