Abstract The compounds Ba 2 LaRu 0.5 Sb 0.5 O 6 and Ba 2 TaRu 0.5 Na 0.5 O 6 have been used to study the magnetic properties of Ru(V) when present in low concentrations in a mixed metal oxide. Ba 2 TaRu 0.5 Na 0.5 O 6 is a simple cubic perovskite ( a 0 = 4.1321(5) A) with a random distribution of Ta, Ru, and Na over the six-coordinate sites and a magnetic susceptibility that follows the Curie-Weiss Law (μ eff 3.44 μ B , θ = - 142 K). Neutron powder diffraction has been used to show that Ba 2 LaRu 0.5 Sb 0.5 O 6 is a distorted perovskite (space group 1 —1, a = 6.0741(5), b 6.0895(5), c = 8.6124(9) A, α = 89.93(1), β = 90.39(1), γ = 89.91(1)°) with a 1:1 ordered arrangement of La and Ru/Sb atoms over the six-coordinate sites. Again the magnetic susceptibility follows a Curie-Weiss law (μ eff 3.78 μ B , θ = -170 K). These results are considered in the light of the magnetic susceptibility of Ba 2 LaRuO 6 (μ eff = 4.00 μ B , θ = -304 K).