The magnetic susceptibilities of some quarternary oxides with the hexagonal barium titanate structure have been measured from 77-900°K. These phases correspond to the formulas Ba 3MTi 2O 9, Ba 3M 2MgO 9, and Ba 3M 2NiO 9, where M = Ru or Ir, and to the formula Ba 3Rh 0.6Ti 2.4O 9. Except for Ba 3Ir 2MgO 9, which had temperature independent susceptibility, the compounds showed Curie-Weiss behavior with large, negative Weiss constants, indicating considerable magnetic interaction between the magnetic ions. The calculated magnetic moments were in reasonable agreement with theory when these magnetic interactions and the large spin-orbit coupling constants of the 4 d and 5 d transition metals were considered. Thus, for Ru(IV) in Ba 3RuTi 2O 9 (θ = -256°) μeff = 2.86 μB, and for Ir(IV) in Ba 3IrTi 2O 9 (θ = -408°) μeff = 1.76 μB.